YOU ASKED THE RIGHT PERSON LOL
Igneous rocks are made up of cooled and hardened lava. Igneous rocks are different depending on where the lava came from. Obsidian and pumice are examples of rocks formed by lava underground. You can notice fine grained (smooth) texture and/or appearance of these rocks compared to igneous rocks that are formed from lava above ground, like basalt.
Check out some books about igneous rocks from your library if you want more detailed information.