A browser is the program that you use to access the internet. It might be Internet Explorer, or it might be Safari, or it might be Firefox, or it might be something else. Internet Explorer is standard with PC's (though you might have downloaded something else) and Safari is standard with Mac's.

The default setting (unless you have changed it) is typically that your browser typically accesses the internet all by itself to check for updates. Sometimes your browser will ask you if you would like to update it if online updates are available. Othertimes your browser will automatically download updates without telling you (all depends on your settings).

If your computer is very old then sometimes updates can make your computer run slower (because updates take up space on your computer). Sometimes updates can alter your browser settings, too. So it might be that your browser has updated and that is why your computer is running slow. It might be that your browser is blocking your accessing chat, too.

You might benefit from running a defragment on your computer...