Double-tap Shift anywhere in the app (or tap the search icon on mobile) to search across every workspace, Domain, repository, and file you've got registered, all at once. See Keeping a growing workspace list tidy for more on managing a growing list.
Your avatar in the top corner opens the account menu — your profile, user management if you're an admin (see Admin & User Profiles), settings, this help area, and a way to switch which context this install is acting as.
Everything in DF Code is namespaced to whichever context is picked, so more than one person can use the same install — a shared machine, a shared network — without anyone stepping on anyone else's work.