Of course, it can be confusing. :)
As you get higher you’ll unlock more features. You unlock the shard shop when you get your first 7 star unit. You unlock the scavenger when you get your first unit to gear 13.
Signals are mainly found in the top Cantina battles. When you get there, you’ll see them. And the game has a nice feature where you can tap on what you’re missing and it will show you where you can currently get it, including for gear and character shards.