Just like upgrading the tires on your car, or adding a turbo to a 4 cyl engine, computers need upgrades.  As software advances our hardware needs to be upgraded,  this process varies from simple to almost impossible. Something simple like upgrading Ram on a PC from 2011 can really help with speed, or switching from a traditional hard drive (HDD) to a Solid State Drive (SSD) can allow you to load the window that facebook uses a bit faster, or even upgrading the graphics card to play PC games.