The Blue Screen of Death, also known as a BSOD or a 'stop' error, may sound bad, but it is usually fixable. When the problem manifests, it completely shuts down your computer, stopping it from working and displaying a blue screen, usually with a message about restarting or a critical error. Your computer will then need to be restarted.
You have several options for resolving this. To begin, check how much free space you have on your system drive and, if it's low, make some space by deleting larger files or programs you don't need. Also, make sure that all of the most recent updates have been applied to the software on your machine, as having outdated apps can sometimes cause problems.
It's also worth noting that if you've overclocked your PC in any way, it's probably a good idea to turn it off if you're still getting BSODs (it could be causing the instability). The exact steps will vary depending on the machine, but if you overclocked your PC yourself, you should (hopefully) know how to reverse it in the BIOS. If it was done by someone else, such as your PC manufacturer, contact the vendor for specific instructions on how to proceed.