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.

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, … ] )

Lookup function in microsoft power apps return only a single record value but Search and Filter function in power apps return set of records.

Lets say we have one datasource “Vehicle”

Vehicle	Capacity
Car	4
Truck	3
Bus	100
Train	1000

Filter( Vehicle, Capacity> 4 ) will return

Vehicle	Capacity
Car	4
Truck	3

LookUp( Vehicle, Vehicle= “Car”, Capacity) will return 4

Search( Vehicle, “Tr”, “Vehicle” )

Vehicle	Capacity
Truck	3
Train	1000