I check my security settings (from my Facebook acc.) from time to time, and sometimes I see there are IP addresses which logged into my account but don't belong to me. When I look in the web who is the owner of this IP address I get info I don't know how to interpret. Does this mean that all those different IP addresses have been trying/logging into my account to hack my privacy?
If you see different IP addresses on Facebook, don't panic.
Some of them are APIs from services you connected to Facebook, like Instagram. Some of them are services that use Facebook to authenticate you.
If you are concerned about someone hacking into your Facebook, you should activate 2-way authentication. With this, you will be informed every time someone tries to log into your account.
The information you do not understand how to interpret? like the WhoIS information? I think you should clarify that a bit more because I am not sure if maybe you are seeing an IPv6 address or something more specific like the information about that IP.
In most all cases involving Facebook, Yes. The addresses are either logged into your account already. possibly a smartphone if you have one and you yourself logged into FB from that phone.
For instance, I use my smartphone to logged into Facebook and Facebook messenger. I live in Arizona, but when I look at my security on Facebook, it shows me an 22.214.171.124 which can make you think "What the heck!?" looking up that UP I can see it is my phone carriers network, that is where the phone is getting its originating IP from. So what looks like a hacker is actually just me.
Sometimes there are APi's that connect to your Facebook which require a session to be active on your account during the time of activity. Which can show up some suspicious IP's. So you can also include that as a factor.
All in all it can be confusing. but if the session on your Facebook is active and its in a completely different state or country you are in. You can definitely accept the fact that they are on your Facebook.
However, most of the time its a bot. I recommended strengthening your password.