"Remember" means to access a memory of something or to have a memory of something: - Do you remember where we went last year? - Yes, to New Zealand. I remember my youth./I remember the 60s./I remember what New York was like in the summer of '72. "Memorize" means to commit something to memory, to make a new memory: Memorize these formulas. You will need to use them in the test. But like I said, you can also use "remember" in this way in more relaxed contexts. For example, you're standing on top of the Eiffel Tower with your boyfriend or girlfriend. You would say: "Let's remember this moment!" It's the same meaning as "memorize", but "memorize" would almost be wrong here because it would sound too formal. "Reminisce" means to actively remember. This is the difference: I remember my youth. VS I'm reminiscing about my youth. The first one is just you stating the fact that you have a memory of or memories from your youth. You're not accessing them right now, you're just saying they exist. The second one, however, is you saying that you're accessing these memories right now. That's also why you couldn't really say: I reminisce about my youth. You could, but that would mean that you do it regularly, that is, that you regularly take the time to actively remember things from your youth. I hope that helped clarify it a bit. :)

Well, they are three quite different words. Just look them up. It should be obvious.