ad, add

Ad is short for advertisement, or commercial--
Did you see the new ad on TV?
Did the ad mention the price?

Add or add ( rhymes with ad ) means to combine into one total, or find the sum of, as in math or arithmetic--
If you add 2 and 2, you get 4.
Did you add up the bill?
Add also means to combine with what you had--
The recipe says to add sugar.
Add may also mean to say something more--
Then she added that she was glad I was leaving.

Now that you know that, you can say--
"Did you add up all the prices in the ad?"

Note--an "adder" is a kind of poisonous snake, having nothing to do with math--
She was bitten by an adder, but survived.
Note # 2--"ads" ( pronounced adz ) is the plural ( more than one ) of "ad"--
These new ads are very clever.
"Adds" ( also pronounced adz ) is the third  person singular ( he, she, it ) form of "add"--
If he adds it up again, he should get the same answer.
Note # 3--not  to be confused with "adze" ( also pronounced adz ), meaning a tool something like an axe--
He used an adze to carve wooden sculptures.