Steps to follow for Launch setup:

1. Create web property in Launch
2. Set up Host
3. Setup environment
4. Install extension
5. Deploy the script in web/mobile app
6. Capture data in context data and use processing rule to map that data into analytics variable in case of mobile
7. Capture the data in data element and put the value of data element in analytics variable
8. Setup Rules
9. Send Beacon
10. Publish the Library

Launch guide : https://docs.adobe.com/content/help/en/launch/using/overview.html

Mobile app implementation guide:https://aep-sdks.gitbook.io/docs/getting-started/create-a-mobile-property

Check this if you are planning to upgrade from DTM to Launch: https://docs.adobe.com/content/help/en/launch/using/reference/upgrade/overview.html