As mentioned you can see the processes running in the task manager.
For windows based os you can stop things from starting up:
click Start then Run then type msconfig hit enter, then click the startup tab. Stuff you don't want running just uncheck. click ok. yes to restart the computer, when it starts back up a pop-up window will open. Click the box that says don't show this on startup (bottom left as I recall. and voila.
It doesn't remove anything from your computer, just stops it from running just because you started windows. Be mindful not to shut your AV or firewall if you have one etc. If you don't know what something is, google it. If you shut something you need later, same steps, but then just add a check instead of removing it.
Kevin