Noob question: When looking at the Seeds and Peers columns of qBittorrent, there are two numbers: one of which is outside the parenthesis and one is inside the parenthesis. Ex 0 (5).
What is the difference between the two numbers in each column?
It's the other way around; you connect to seeders.
In the example of 2 (3), there are 3 total seeders and you're connected to 2 of them.
Although in your screenshot, you're at 100%, so you're not connected to any seeders at the moment and are, yourself, a seeder. You have peers (leechers) connecting to you. Same principle applies; in an example of 2 (7), there are 7 peers in total, and 2 of them are actively leeching off you.
That's why the non-parentheses number is zero for all seeded torrents. In parentheses number is "hey I'm here". Out of parentheses number is "hey I'm here. Let me in."
For actively downloading torrents they're an indication of connection health. If there's 150 announced seeders but you only open a connection to one or two of them, you might have a network problem.