SELECT permission is required to read data from table
GRANT SELECT ON OBJECT::dbo.TableName TO UserName;
INSERT permission for writing to a table
GRANT INSERT ON OBJECT::dbo. TableName TO UserName;
UPDATE permission to change an existing role
GRANT UPDATE ON OBJECT::dbo. TableName TO UserName;
DELETE permission is required to remove a row
GRANT DELETE ON OBJECT::dbo. TableName TO UserName;
Check out the following link this will help you to find all permissions for users in a database:
SQL Server query to find all permissions/access for all users in a database - Stack Overflow