Every record in Beagle belongs to a firm, so the first thing Beagle asks after sign-in is which firm you are working in.
#Choose a firm
The Choose a Firm screen invites you to "Choose the firm you want to open now." Firms you belong to are listed under Available Firms, and the one you are in is marked Currently Selected. Each entry shows its licence status, so you can see at a glance which firm carries your access.
#Accept an invitation
While the screen loads it reports "Checking for invitations…". If somebody has invited you to their firm, it appears here with an Accept action. Accepting adds you to that firm; it does not move any of your existing records into it.
#Create your first firm
If you belong to none, Beagle offers Create Your First Firm. Enter a Firm Name and choose Create Firm — the button reads Creating Firm... while it works.
Choose the name carefully. It is the name your firm's records live under, and it is what other members will see when they are invited.
#Switching later
You are not locked in. The firm can be changed after sign-in, and records stay with the firm they were created in — switching changes what you are looking at, not where anything lives.