Your "close friends" are the friends that you spend the most time with and feel most comfortable with.

English speakers also use the phrase "best friend", but the word "best" usually refers to only one thing. So you can use "best friend" to talk about the one friend who you are closer to than any other friends. But it's a little strange to say "my best friends".

You can think of the circle of people that you know as falling into these groups:

1. your best friend (just one, technically, but sometimes people use this for more than one person)
2. your close friends
3. your friends
4. acquaintances (notice that I didn't say "your acquaintances" because we don't "own" acquaintances. You describe someone as being "an acquaintance", not "my acquaintance".