when you have an the word "add" on your rx prescription, such as 4.00. does that mean that the power is on the bottom of the lenses only for reading? does the word add mean bifocal? i have an add 4 and i was wondering if it will just be the strength on the bottom of the lense

I think that just means you will be getting a bifocal, and that's going to be the bottom part of the lens.

Add powers are commonly between +1.00 to +3.00

If your add power was +4.00 the reading portion (the bottom part of bifocal/multifocal) lenses would only be +4.00 if you required no further correction. Since many people do need further correction this is usually not the case. The add power is literally added on to the first number in your prescription (sphere number). The number is used to calculate the prescription in the bottom of your lenses..... it is not the actual prescription in the bottom of your lenses
Add does not mean bifocal... but it does mean you require a different correction for reading so that is why you will need reading glasses or bifocal/multifocal lenses.... and no it is unlikely the bottom portion of your lenses will be +4.00 unless you require no other prescription then your add power!
Hope this helps