You can join any Corp that belongs to your faction or a Corp from another faction that has captured a station in the region where your Homebase is located. Additionally, if a Corp CEO has a Homebase in the same constellation as yours, you can also join that Corp.
You can follow the below steps to join a Corp:
- Find the Corp Menu on your Main menu
- Click on the Join button.
- You are now a member of the selected Corp.