Tensor index notation with e.g. square brackets

I want to learn playing with indices and some notation in General relativity. But in every book just is used this notation. I know upper and lower but I don"t know the meaning of some combination of these indices, like when we have 3 indices in both side of the letter in bracket (e.g of the form $\partial_{[a}F_{bc]}$).

Could you please explain me or suggest a book that say almost everything , for example, when we need to put 2 indices in a tensor, one up and one of them down, ...?