Draw a number line. Don't be lazy, really draw and put numbers and arrows on it.
One number is 5, find 5 on you line and make it dot bigger.
The distance between two numbers is 4. Now look at the line, you have a number, 5, and you need another number, which is 4 away from 5.
Note that the number line extends from 5 in two directions. You could have a number on the left, 4 from 5 gives you 1, or you could have a number on the right, 4 from 5 gives you 9.
In equation forms, it is |? - 5| = 4, to solve for ?, you have two answers.