What do you want to do back up on? The system, personal file och everything?
Easyest way is to use a external harddrive and just copy your personal file on to it, but a hardrive/memory stick is not the safest way to do all the time as it can crash, you lose it or someone steal it. You can always save you data on a cloud servic, its not so hard and most cloud base company explain how you fo when you sign up for it. Depending on how safe you want to be two backups as best, one cloud/online and one external harddrive. Moste system have build in options for system backups, personal data you may have to chose yourself what to backup. There are free programs online to test what you like the most, and many programs you can do setups in so they auto backup folders on you pc to cloud/online or external harddrives.
Its all depend on what system you are running or what you want to do backups on.