Select

Select[data, crit] picks out all elements ei of data for which crit[ei] is True.

Select[data, crit, n] picks out the first n elements for which crit[ei] is True.

Select[crit] represents an operator form of Select that can be applied to an expression.

Examples

Select even numbers:

Select[{1, 2, 3, 4, 5, 6}, EvenQ]
(* {2, 4, 6} *)

Select with a custom condition:

Select[{-3, -1, 0, 2, 5}, # > 0 &]
(* {2, 5} *)

Please visit the official Wolfram Language Reference for more details.