Fortunately, Google's tools make it far less of a crapshoot when you first launch a new campaign or ad group.
Manual bids are the best way to understand firsthand how your dollars are working (or not working) for you.
Start with fundamentals -- numbers that you can personally see, respond to and adjust.
You'll need to be getting at least 50 conversions a month (at the campaign level) before you start using automated bidding.
Google Display Network (GDN) campaigns can be a bit complicated.
For now, let's focus on Search.