StringCases

StringCases["string", patt] gives a list of substrings that match the pattern.

StringCases["string", lhs -> rhs] gives a list of rhs values for matching substrings.

Examples

Find matching substrings:

StringCases["the cat and the hat", "the"]
(* {"the", "the"} *)

With pattern:

StringCases["a1b2c3", DigitCharacter]
(* {"1", "2", "3"} *)

Please visit the official Wolfram Language Reference for more details.