Apply

f @@ expr or Apply[f, expr] replaces the head of expr by f.

f @@@ expr or Apply[f, expr, {1}] replaces heads at level 1 of expr by f.

Apply[f, expr, levelspec] replaces heads in parts of expr specified by levelspec.

Apply[f] represents an operator form of Apply that can be applied to an expression.

Examples

Apply Plus to sum a list:

Plus @@ {1, 2, 3, 4}
(* 10 *)

Apply at level 1:

f @@@ {{a, b}, {c, d}}
(* {f[a, b], f[c, d]} *)

Please visit the official Wolfram Language Reference for more details.