Most of us want to feel somewhat safe. So do computers.
Safe Mode is a situation that your computer boots up into when it thinks that "something is very wrong". Something isn't always wrong, however.
If we are having problems with drivers, or we had a "big-time" crash while using a program, the computer may restart in Safe Mode.
When a computer starts in Safe Mode it only loads the minimal set of drivers possible to run, as well as the base settings for the video card and other hardware. This is a troubleshooting mode.
We can put all of the fancy additions on our computer and have great performance. We can add, and change video drivers. We can do a lot of things. When we push the envelope there is always a chance we are going to pierce the veil of instability and overrun our limitations. If this happens we may not be able to restart our computer at all.
If we get blocked out of our computer we can hope it will start in Safe Mode so we can straighten everything out. If it does not start in Safe Mode we will have to press the F5 key on startup or utilize the F8 Boot Options and make the selection ourselves.
Once we are in Safe Mode we can reverse our changes, or make different changes, and restart our computer. If the changes are acceptable the computer will restart normally. If we haven't done anything and we started in Safe Mode, it is probably because our computer crashed pretty hard. It would do us well to just restart the computer. This will probably take care of things.
If it doesn't, you are going to have to tinker around until you get things to a functional base state. Try a modification (video driver, setting, or missing file, etc.) in Safe Mode and restart. Repeat. Sooner or later you should "land" a happy configuration.