2012 iMac Internet Connect Issue

Looking for some help here. I recently bought a 2012 iMac—I know it’s old, but I really like this model. It’s currently running OS X 10.8.5, and for some reason I can’t get it to properly connect to the internet. I was able to install Google Chrome, but websites only half-load and I keep getting “couldn’t establish a secure connection.” Safari doesn’t work at all, so I can’t sign into my Apple account or update the software. I only paid $75 for it, but it just seems odd that the internet works partially on Chrome yet not at all on Safari.