Capitalize

Capitalize[string] yields a string in which the first character has been made uppercase.

Capitalize[string, scheme] gives a string capitalized using the specified capitalization scheme.

Examples

Capitalize first letter:

Capitalize["hello world"]
(* "Hello world" *)

Title case:

Capitalize["hello world", "TitleCase"]
(* "Hello World" *)

Please visit the official Wolfram Language Reference for more details.