What is best way for me to back up my pc?
I do pay for icloud storage....
This is not an easy question to answer as it can involve many factors.
Typically, the most common way for someone to backup a computer is to buy an external USB drive and then use some sort of backup program to backup the computer to the external drive.
Depending on your usage pattern of your computer (i.e. if you really don't have a lot of personal files such as pictures, videos, word processing files), however, that might be a little bit of overkill.
And that is the essentially one of the most simplistic ways. Depending on your tolerance for risk, your overall risk level for things like malware (i.e. do you stick to just a few "big name" websites...or do you wander over all kind of sites on the Internet), your willingness to spend money, and how important you consider your data, you might choose to go even more complicated from there (i.e. multiple backups, keeping at least one backup off site, etc).
So, you might want to expand a bit on your usage.
What OS are you using? This might help determine if you have a viable backup program built into your OS.
What size is your hard drive? And how full is the hard drive (i.e. how much data do you have)? What type of personal files do you have (i.e. pictures, word processing documents, spreadsheets, home videos, bought videos, etc)?
How do you use the computer? Just browsing mostly and other online stuff? Or do you do a lot of "content creation" on your computer?
Do you want the backup just to protect your user files? Or do you want your backup to be able to restore the computer to functioning without having to reinstall Windows and the programs? And if you want your backup to be able to restore the computer to functioning condition without reinstalling Windows and programs, do you want that to be pretty much immediate or is it OK if takes a little time?
How much do you want to spend on setting up a backup "system"?
The one thing that I will note is that generally speaking iCloud is not terribly conducive to backing up Windows computers. If your computer in a Mac running the latest version of the macOS (aka Sierra or 10.12.x), then it can be more useful in effectively, kind of backing up your Mac...but not with earlier versions of the macOS. There are likely ways to "kludge" using iCloud to backup Windows and older versions of the macOS, but it would not be ideal.