Simply hover your mouse cursor above the said options.
The tooltip will tell you what they mean exactly.
In my opinion:
Use proxy for peer connections - Turn ON. If this is not ticked, the traffic to peers, like other people/peers will simply go through your normal connection. Your proxy IP will show up on the tracker, but your own IP will transfer data.
Use proxy only for torrents - Turn OFF. Should not make a big impact, like RSS traffic is negligible and should work just fine. If your proxy causes issues to these functionalities, turn ON the box.
IF you don't tick any of the boxes: qBittorrent will contact trackers with your proxy, but will transfer data directly to-from people with your normal IP/connection. And it will use your normal connection for RSS, checking for new version, that sort of stuff.
Ps.: Most tracker software I saw kept all their connections in memory, so honestly, there is not much point in using a proxy without "peer connection" on. Like, without that, only the tracker will receive the proxy IP and no one can check out the current peers because if the server gets taken, they get shut down and all the data in the memory will be simply lost.