Filter function in Microsoft POWER APPS : The Filter function finds records in a table that satisfy a formula. Use Filter to find a set of records that match one or more criteria and to discard those that don’t.
Filter( Table, Formula1 [, Formula2, … ] )
Lookup function in Microsoft POWER APPS :The LookUp function finds the first record in a table that satisfies a formula. Use LookUp to find a single record that matches one or more criteria.
LookUp( Table, Formula [, ReductionFormula ] )
Search function in Microsoft POWER APPS :The Search function finds records in a table that contain a string in one of their columns. The string may occur anywhere within the column
Search( Table, SearchString, Column1 [, Column2, … ] )