Hey Kevin! Great question! Every time a rocket is launched into space, parts of it are left behind in orbit. There's a really cool website that lets you visualize all the space junk at http://stuffin.space/ The sizes of each piece of junk are greatly exaggerated on this website, but you can see how many there are! Until recently, people haven't thought much about how we can clean up Earth's orbit. Some strategies people have employed to keep space clearer are: make sure a spacecraft has the fuel to either crash back into Earth when it's old, or go higher in orbit (where it will be moving slower and there's also more room), or put it low enough in space that it's still just slightly in Earth's atmosphere, which will slow it down over the course of ~10 years and make it fall back to Earth regardless of whether the satellite still works (SpaceX's new Starlink satellites use this strategy).

A more advanced technique would be to use a trash-collector satellite that could go find pieces of space junk and throw them back to Earth, like Japan's recently-launched Elsa-D satellite (you can read more about it here! https://asia.nikkei.com/Business/Aerospace-Defense/Japan-s-Astroscale-launches-space-debris-removal-satellite )