because is actually a lot like the chinese yin wei but in english you can't start a sentence with because. " i didn't go to school because, i was sick. since is almost like because but not really since it can be used in more ways, i.e " ever since i could remember I've had blond hair. or since i was sick i didn't go to class. but the second one example is more British than American. As is more for comparison: he is as cute as a puppy. she's as sweet as pie. For: can't explain so I'll just use examples, i bought the drink for my friend. I had to do a project for my English class. we had pizza for lunch.

In my opinion what my teachers taught me according to their teaching materials was a bunch of bs, don't really rely on it, it was just complicating the mess.

Don't use "for" as a conjunction yourself, if others use it, well, let it be. When you feel like saying "由于，既然" in your Chinese thinking about the situation, you choose "since", simply wanting to say "因为" in most cases, you say "because". Well, the most tough one to explain you is the "as", a pain in the ass... you gotta figure it out yourself, the "tone", sounds kind of like "随着，既然我一直以来……" or something like it...