Generally the web is pretty safe. Windows comes with a fairly competent defense system and so long as you are not retarded you won't really be dealing with viruses. My best advice is to
1. download a good adblocker, ublockorigins is the gold standard right now.
2. use firefox, crome is a huge target and any kind of active exploit will start by targeting there. Also firefox isn't litterally run by an ad company trying to force you to see ads so....
3. If you DO want to download something sketchy(like a pirated game), get a sandboxing tool and run it sandboxed first. Look for anything weird happening (like tons of ram use while idle) and if you sense something off, assume its a trap
4. Back up occasionally and keep your backups airgapped (unconnected to your system) when not being accessed.
The VAST majority of viruses are crypto miners now, so if your computer is running sluggish it might be something like that. Finding it is as simple as opening up your task manager and looking for the weirdly resource intensive program and removing it. The days of randomly taking over your pc are gone