The Patterns tab has four sections. Three of them are lists of patterns you have a relationship with; the fourth is all of Ravelry.
Library — what you own
Patterns you have: synced from your Ravelry library, imported as PDFs, or saved from a link. This is the “what could I make tonight” list.
Favorites — what you’ve fallen for
Patterns you’ve bookmarked. You might own them, you might not — a favourite is “remember this”, not “I have this”.
Saved without a Ravelry account, favourites live on your device. With an account they’re your Ravelry favourites, in both directions.
Queue — what’s next
What you’re planning to make, from your Ravelry queue. This section needs a Ravelry account and doesn’t appear without one.
A pattern can be in more than one
Library and Favourites aren’t exclusive. Owning something and loving it are different facts, and a pattern you own and adore sits in both — that’s working as intended, not a duplicate.
If you’re wondering why the same pattern appears twice within one list, that’s something else — see Why do I see a pattern twice?.
Search — everything else
The fourth section searches the whole of Ravelry, not just your own patterns, with filters for craft, category and more. It works without an account.
That’s the one to use when you don’t want something you already have — you want something new. See Filtering and finding patterns.