I've been using LeafSnap for a while, and it's done ok, except for a little while a few weeks ago when their primary server went down.
I started a thread a while back for ID App reviews, but turns out there are only a half dozen worth mentioning right now, so it didn't last long.
LeafSnap lets you take a fresh pic or upload one from your phone storage, then select what aspect of the plant the AI should be looking at: Leaf, Bark, Flower, or Fruit. Then, like
@Glaucus explained, gives you a list of possibilities to compare to.
Ad subsidized, which can be annoying, but I never get bugged about buying the pro version.
If you're using the app, you don't know what the plant is you're looking at--how do you know the app is correct? Not trying to be a smartass, just wondering...
You can also try it out on plants you already know about as a test.