They are completely different. I'm going to give examples of the single most common meaning of each word, and explain the examples. "Accept" is a verb. 1a) The store accepts cash. 1b) The Olympic athlete accepted the prize with joy. "Accept" means "to receive with pleasure," or "to agree to receive." "Except" is a preposition. The pronunciation is almost the same, sometimes EXACTLY the same, as "accept." But they are different words with different meanings. 2a) The meter is the standard unit of length everywhere in the world except Liberia, Myanmar, and the United States. 2b) Our public library is open every day except Sunday. "Except" means "with the exclusion of" or "other than." (It can also, rarely, be a verb, meaning "to exclude" or "leave out.") "Exact" is an adjective meaning "precise," "accurate," "totally in accord with." 3a) A meter is exactly 100 centimeters. Not 99.9, not 100.1, exactly 100. 3b) Your answer is perfect. It is exactly right. (Rarely, "to exact" can be a verb meaning to force someone to pay money or comply with an agreement).

in my terms, Accept means to agree or accept something Except means without something/someone or not include something/someone Accept: I can't accept this behavior. I accepted his friend request ;) Except: I invited everyone except Julia. She ate everything except garlic.

I would add to Dan's excellent answer that "except" can also serve as a conjunction.