What is the difference between signed and unsigned integer.Can any one help me?

Simple: one can contain negative values, the other can't.

To expand a little, a signed value uses one bit (usually the top, or most significant bit) to indicate if the number is positive or negative, and an unsigned integer uses all available bits for the number - so the number of different values that can be held is the same, but the range of values is different.
Assume we used a 4 bit processor (to make the numbers easier)
Unsigned:

Bits   Value (decimal)
0000     0
0001     1
0010     2
0011     3
0100     4
0101     5
0110     6
0111     7
1000     8
1001     9
1010    10
1011    11
1100    12
1101    13
1110    14
1111    15

Signed:

Bits   Value (decimal)
0000     0
0001     1
0010     2
0011     3
0100     4
0101     5
0110     6
0111     7
1000    -8
1001    -7
1010    -6
1011    -5
1100    -4
1101    -3
1110    -2
1111    -1

-8 in this scheme is sometimes treated as "minus zero" but you can probably ignore that!