How to check the security of a computer, home Wi-Fi network?

Question

WiFi

Good day,
Tell me how to check your computer, WiFi network, etc., etc. for security: viruses, hacks, etc., etc.
1. About 3 years ago, it’s not clear how, $ 100 was withdrawn from my PayPal account, the money was then returned, IP was from where either from Latvia, or from Lithuania, before that PayPal used it only 2-3 times. Since that time, that PayPal account has closed.
2. About 2 years ago, it is not clear how, someone got into my one of several gmail accounts, which the latter immediately notified me about this, the IP was from somewhere in the states. 2FA and sms verification were not installed on that email back then.
3. Literally 2 weeks ago, a new friend stayed overnight, and in the morning she had a message on her phone that someone was trying to log into her gmail, but because there was an SMS confirmation, it seems that they could not.
4. Yesterday my roommate told me that someone took $100 from him at the weekend from a new card at a gas station, either with Visa or Master'a - he didn't ask, but the cat. he received just recently. It all happened on Saturday night while he went with friends somewhere to hang out.
I don’t know now if it’s all connected with my computer or network (although my friend didn’t connect to the network, it seems, although I’m not 100% sure, I also had it before), but I get the feeling that MB someone then somewhere I hacked either my Mac through some other WiFi (I often connect my computer to public networks in all sorts of cafes, libraries, etc.), or I immediately have access to my WiFi (although literally 2 months ago I also changed the provider), or, well on kraynyak, mb already in general what thread of special services or hackers personally graze me?
Mb, of course, all paranoia and pure coincidence, of course, but somehow everything is very suspicious.
Those. The question is how to check everything, who has good links: what to read / watch / do on this topic?
And yes, also by the way: Somewhere about 2 years ago I started learning to program and before that terminals, all sorts of brew, etc., especially I never used it in my life, but about 2 years ago, when I started, I didn’t do anything on it ( knowing and not knowing, but more than the second) and mb some ports are still open somewhere / access to something, etc., which is still, that mb is also connected. Yes, the phone also just updated 2 months ago.