Ok so i thought I understood the seed growing stuff so I planted some Banana after watering it a couple days I got this I'll be honest. Idk what to do with this thing. Please help.

It looks like this one can be used as a toy for your pet. Some of the rarer seeds like can give you stuff or do things like increase a pet's stats.

If you're not familiar already, I would recommend saving this site SubetaLodge to your bookmarks, they are a wonderful fansite for Subeta that has a lot of extra info on what some items can be used for if you search for that particular item (if it has any special use options, or info on where it came from, etc.).

https://www.subetalodge.us/

If it doesn't have anything special listed in the notes section when you search for it, then it probably doesn't have anything special about it. Some items just kind of exist and can't really be used for anything in particular except for like putting them in pet treasures or sometimes quest givers will ask for them in their quests.