Simbrief in most cases will automatically assign you a departure procedure route called a SID (Standard Instrument Departure) in your flight plan when you set it up - exceptions may be if the airport doesn’t have any departure routes (in your direction of travel or at all).
When you import the flight plan into Infinite Flight, the departure route should appear with a green bracket in the FPL bar on the map screen.
Airports that lack SID like EGTC etc, are usually vectored by atc after initial runway heading and that means you will need to add a waypoint to connect your route here’s an example.
