App Campaigns (formerly UAC) take your creative assets, a conversion goal and a bid or target, and let Google’s system decide where and to whom to show ads. You choose what counts as a conversion — installs, an in-app action, or value — and the system finds more of it.
They are not Search campaigns for apps. You cannot bid on specific queries or cleanly separate intent. If you optimise for installs and CPI falls, the system has done what you asked; whether it found better users is a separate question to answer with cohort data.