The Pikmin series consists of three games so far (plus Hey! Pikmin, which doesn’t fit in with the core play of the other games, and the Pikmin subgame in Nintendo Land, which is extremely non-canonical), and so like any story-driven game property that’s survived for awhile it’s accreted a shell of lore that new players may feel like they have to break through if they want to fully enjoy it.
There’s a whole genre of explainer videos on Youtube to help players crack into these nuts, of various degrees of quality and/or sarcastic intent. Many of them are hyper-edited and obnoxious, and so I’m reluctant to link to them, but the one embedded above, from Chase Kip, is relatively chill and entertaining. So if you want to know what the heck is up with these Pikmin games, please check it out. Despite the thumbnail, it really isn’t about Olimar and the Pikmin’s sculpted bodies, at least, not that much.
(As is Nintendo’s style, each game doesn’t really require past knowledge to understand, as they not only explain everything that needs to be explained within the game itself, but even contains a tutorial that previous players will have to get through to re-teach them everything they’ve learned before. But, this doesn’t stop some people from feeling like if they start playing in the middle of a series like they’ve missed out on something.)