To a native speaker, the difference is very clear.
accept [æksɛpt] / except [ɛksɛpt]
For English learners, one difficulty is that English has a lot of vowels. For example, some languages have five vowels, /i/, /e/, /a/, /o/, and /u/, whereas North American English has about 14 depending on the dialect. Consider these words: beet, bit, bait, bet, bat, bot, but, boat, book, boot, bout, and bite. A learner from a language with the five vowels mentioned above will usually confuse beet/bit, bet/bat, bot/but, and book/boot. The pair bet/bat is the same difference as except/accept.