I will explain how to understand them, and YOU write the paragraph!
Make yourself a number line with increments. On the right hand side of the number line, place your zero. Then start placing negative numbers to the left of the zero starting with -1.
-10 -9 -8 -7 -6 -5 ....... 0
When we add negative numbers, we are moving to the left on the number line. For example, add -1 and -4. We do this by seeing that if we start at -1 on the number line, we are now going to move even further away from zero because -4 is not a positive number. Move 4 spaces to the left and you are at -5.
Doesn't matter how big (small really!) your negative numbers are, the principal is the same.
Just to make sure you understand, what would you get if you added +4 to the -1? Notice how you will be moving toward the positive side of the number line when adding a positive number.
Hope that helps. If not, check out http://www.cimt.plymouth.ac.uk/projects/mepres/book7/bk7i15/bk7_15i1.htm