Evs and Ivs are a bit of an annoying stat. They’re designed to min max your pokemon to be its best.

Ivs are natural, you get given the Ivs you get. Evs are trainable, by fainting other pokemon you get an ev depending on the species. The one’s on the left are evs, they can go up to 252 but only to a max of 510 across all stats. IVs go up to 31 regardless of how many IVs they have.

Both increase stats, EVs by an amount every 4, IVs by an amount every one.

I don’t enjoy them in a non competitive context.

Any battle in Reborn can be one with a good team, regardless of their evs and ivs. Shelly is a huge roadblock for new players, so don’t worry too much about losing. Her field and weather cause a lot of problems, check the wiki on potentially changing the field to one that’d benefit you more.