The word not is an adverb that modifies a verb. The adverb not is always placed between the verb and a helping verb, like this: I did not call last night. The verb is did call. The adverb not modifies the verb.
We can make the helping verb did and the adverb not into one word by bumping out some letters and adding an apostrophe. The words did not become the contraction didn’t.
Here are more contractions with the adverb not:
can not = can’t
should not = shouldn’t
would not = wouldn’t
could not = couldn’t
is not = isn’t
was not = wasn’t
Make a contraction with a helping verb and the adverb not by bumping out some letters and inserting an apostrophe.
▶Now you try it. Make a contraction out of two words in this sentence. I did not walk the dog today. Did you make the word didn’t? Good for you