"No" is a negative response, simply the opposite of yes (generally). If someone were to ask if you wanted something to drink, "no" would indicate that you didn't want a drink. If you were to reply "yes", then it indicates that you do want a drink.
It can be used in other ways, however. For example, if a parent wished to punish a child for bad behaviour, they might tell them "No more sweets", which means that the child isn't allowed any sweets. If a cinema had sold all their popcorn, they would tell customers "There is no popcorn left".
"Not" has a similar meaning to "no" but they are used in very different ways. "Not" refers to the past. If something is not complete, for example homework, then it has not been completed. It is used to say that something hasn't happened. For example:
"I have not driven a car recently."
"I have not eaten a lot today."
In both of those examples, if the word "not" were to be missed out, the sentences would mean that I have driven a car recently, and I did eat a lot today.
It's difficult to describe what "not" means without actually using it in the explanation, so I hope you understand.
Interested in Language