Please explain how to do long multiplication. 
Long multiplication is a way to multiply numbers with 2 or more digits.
Here is an example of a long multiplication of two 2digit numbers:
37 × 28
First, set out the two numbers in columns like this:
3  7  
×  2  8  
Then (being careful with the columns) work out 8 times 37:
8 × 7 = 56: 
 then  8 × 3 = 24: 

Place a zero in the rightmost column on the next row,
3  7  
×  2  8  
2  9  6  
0  
then work out 2 times 37:
2 × 7 = 14: 
 then  2 × 3 = 6: 

Finally, add these two rows of working out:
3  7  
×  2  8  
2  9  6  
7  4  0  
1  0  3  6 
1  
The answer is:
37 × 28 = 1036 
To work out 37 × 28 you have separately multiplied
37 × 8 and 37 × 20.
In the second row you worked out 37 × 2 and this explains
the extra 0 you had to put at the end.