After catching Budew in the wild (in many different places across the games) or hatching it from an egg, it will need to evolve into Roselia before it's of any use in battle. In order to do this, you'll need to be nice to it and treat it well. This is because Budew evolves with a high friendship level!

What level will Budew evolve?

Budew (Japanese: スボミー Subomie) is a dual-type Grass/Poison baby Pokémon introduced in Generation IV. It evolves into Roselia when leveled up with high friendship during the day, which evolves into Roserade when exposed to a Shiny Stone.

Is Budew worth training?

As for Budew, yes - it is a good Pokemon at the start. Especially if you chose Chimchar. In fact, it's practically essential in beating Roark, so it's worth picking up for that.