TextPosition

TextPosition[text,form] gives a list of the starting and ending positions at which instances of form occur in text.

TextPosition[text,{form1,form2,…}] gives an association of results for all the types formi.

TextPosition[text,formspec,n] gives the positions of the first n cases found.

Examples

Find positions of a word:

TextPosition["The quick brown fox", "Word"]
(* {{1, 3}, {5, 9}, {11, 15}, {17, 19}} *)

Find sentence positions:

TextPosition["Hello world. How are you?", "Sentence"]
(* {{1, 12}, {14, 26}} *)

Please visit the official Wolfram Language Reference for more details.