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.
That is for finding things across everything. For finding a word on the page in front of you, Cmd/Ctrl+F opens a find bar that works the way a browser's does — every match highlighted, counted, and steppable — which the desktop app would otherwise have no equivalent of.
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 Frontier 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.