My school didn't teach B-trees, though they did teach 2-4 trees. I've never really been in a situation where I've needed to use a B-tree; and, I was an accomplished competition programmer in college.
That said, I looked up on the internet what they were and it was pretty easy to follow.
There are some problems that require efficient reading, which is from the disk; and some that require efficient writing --- though that's more of just "buffer your outputs and don't use complex print methods, like System.out.printf"
That said, I looked up on the internet what they were and it was pretty easy to follow.