See the following KB article for the steps to connect Zwift with Strava:
Once the two services are connected, you should be able to sync your data from Zwift to Strava directly each time you end a ride.
Zwift will prompt you with an option to "Save + Strava" at the end of your ride. Just choose that option to send your ride activity data to Strava for further analysis.
This is a one-time setup and Zwift will remain connected to Strava until you choose to disconnect the two services from each other (but why would you do that?!)