Whole number operations
Line up the place values first, then carry or borrow one whole group at a time between columns.
A worked example
For 265 + 178, the ones give 5 + 8 = 13, so write 3 and carry a ten; the tens give 6 + 7 + 1 = 14, so write 4 and carry a hundred, leaving 443.
The mistake people actually make
When subtracting, borrow from the next column instead of taking the smaller digit from the larger one in each column.