How call a SQL Server stored procedure with parameter(s)?

Manfred gave you a good link too :)

Here is an example in c# calling the stored procedure defined below.
The code illustrates both input and output variables from the stored procedure:

public static bool PostalAreaInsert( SqlConnection sqlConnection, ref Guid oid, ref DateTime? registeredTime, ref Guid? registeredBy, Guid? region, string name, DateTime? fromTime, DateTime? throughTime)
        {
            bool result = false;
            SqlCommand sqlCommand = sqlConnection.CreateCommand( );
            using( sqlCommand )
            {
                sqlCommand.CommandText = "PostalAreaInsert";
                sqlCommand.CommandType = CommandType.StoredProcedure;
                SqlParameter oidParameter = 
                   sqlCommand.Parameters.Add(new SqlParameter("@Oid",
                         SqlDbType.UniqueIdentifier));
                oidParameter.Direction = ParameterDirection.InputOutput;
                oidParameter.Value = oid;
                SqlParameter registeredTimeParameter =
                     sqlCommand.Parameters.Add(new SqlParameter
                        ("@RegisteredTime", SqlDbType.DateTime));
                registeredTimeParameter.Direction =
                      ParameterDirection.InputOutput;
                if( registeredTime.HasValue )
                {
                    registeredTimeParameter.Value = 
                        registeredTime.Value;
                }
                else
                {
                    registeredTimeParameter.Value = DBNull.Value;
                }
                SqlParameter registeredByParameter = 
                          sqlCommand.Parameters.Add(
                            new SqlParameter("@RegisteredBy", 
                              SqlDbType.UniqueIdentifier));
                registeredByParameter.Direction = 
                          ParameterDirection.InputOutput;
                if( ( registeredBy.HasValue ) 
                   && ( registeredBy.Value != Guid.Empty ) )
                {
                    registeredByParameter.Value = registeredBy.Value;
                }
                else
                {
                    registeredByParameter.Value = DBNull.Value;
                }
                SqlParameter objectTypeParameter = 
                     sqlCommand.Parameters.Add(
                       new SqlParameter("@ObjectType", SqlDbType.Int));
                objectTypeParameter.Direction = 
                     ParameterDirection.InputOutput;
                objectTypeParameter.Value = 2;
                SqlParameter regionParameter = 
                      sqlCommand.Parameters.Add(
                         new SqlParameter("@Region", 
                            SqlDbType.UniqueIdentifier));
                if( ( region.HasValue ) 
                    && ( region.Value != Guid.Empty ) )
                {
                    regionParameter.Value = region.Value;
                }
                else
                {
                    regionParameter.Value = DBNull.Value;
                }
                SqlParameter nameParameter = 
                    sqlCommand.Parameters.Add(
                      new SqlParameter("@Name", 
                        SqlDbType.NVarChar, 255));
                if(( name != null )
                   &&( name.Length > 0 ))
                {
                    nameParameter.Value = name;
                }
                else
                {
                    nameParameter.Value = DBNull.Value;
                }
                SqlParameter fromTimeParameter = 
                    sqlCommand.Parameters.Add(
                      new SqlParameter("@FromTime", 
                        SqlDbType.DateTime));
                if( fromTime.HasValue )
                {
                    fromTimeParameter.Value = fromTime.Value;
                }
                else
                {
                    fromTimeParameter.Value = DBNull.Value;
                }
                SqlParameter throughTimeParameter = 
                     sqlCommand.Parameters.Add(
                         new SqlParameter("@ThroughTime", 
                                    SqlDbType.DateTime));
                if( throughTime.HasValue )
                {
                    throughTimeParameter.Value = throughTime.Value;
                }
                else
                {
                    throughTimeParameter.Value = DBNull.Value;
                }

                int rowsAffected = sqlCommand.ExecuteNonQuery();
                if(rowsAffected == 1)
                {
                    Guid newOid = (Guid)oidParameter.Value;
                    DateTime regTime = 
                         Convert.ToDateTime(registeredTimeParameter.Value);
                    Guid regByOid = (Guid)registeredByParameter.Value;
                    oid = newOid;
                    registeredTime = regTime;
                    registeredBy = regByOid;
                    result = true;
                }
            }
            return result;
        }

The stored procedure - please note the handling of transactions vs savepoints; it ensures that the procedure will only rollback its own modifications - something that's useful if the procedure can be called from another stored procedure too:

CREATE PROCEDURE [PostalAreaInsert]
  @Oid uniqueidentifier OUTPUT,
  @RegisteredTime DateTime OUTPUT,
  @RegisteredBy uniqueidentifier OUTPUT,
  @ObjectType int OUTPUT,
  @Region uniqueidentifier,
  @Name nvarchar(255),
  @FromTime DateTime,
  @ThroughTime DateTime
AS
  BEGIN
    IF @Oid IS NULL
    BEGIN
      SET @Oid = NEWID()
    END
    IF @ObjectType IS NULL
    BEGIN
      SET @ObjectType = 2
    END
    IF @RegisteredBy IS NULL
    BEGIN
      SET @RegisteredBy = (SELECT Oid From SecurityLogin WHERE [Identity] = SYSTEM_USER)
    END
    IF @RegisteredTime IS NULL
    BEGIN
      SET @RegisteredTime = SYSDATETIME()
    END
    DECLARE @TranCounter INT;
    SET @TranCounter = @@TRANCOUNT;
    IF @TranCounter > 0
      SAVE TRANSACTION SavePoint2;
    ELSE
      BEGIN TRANSACTION;
    BEGIN TRY
      INSERT INTO Element(Oid,OptimisticLockField,RegisteredBy,RegisteredTime,ObjectType)
          VALUES(@Oid,0,@RegisteredBy,@RegisteredTime,@ObjectType);
      INSERT INTO [PostalArea](Oid, [Region], [Name], [FromTime], [ThroughTime])
          VALUES(@Oid, @Region, @Name, @FromTime, @ThroughTime);
      IF @TranCounter = 0
          COMMIT TRANSACTION;
    END TRY
    BEGIN CATCH
        DECLARE @ErrorMessage NVARCHAR(4000);
        DECLARE @ErrorSeverity INT;
        DECLARE @ErrorState INT;
        SELECT @ErrorMessage = ERROR_MESSAGE(),
            @ErrorSeverity = ERROR_SEVERITY(),
            @ErrorState = ERROR_STATE();
        IF @TranCounter = 0
          ROLLBACK TRANSACTION;
        ELSE
          IF XACT_STATE() <> -1
            ROLLBACK TRANSACTION SavePoint2;
        RAISERROR(
            @ErrorMessage,
            @ErrorSeverity,
            @ErrorState);
    END CATCH
  END
GO

Regards
Espen Harlinn