Both Joanne (post #5) and Dini (post #10) gave very clear instructions. I don't know where on this site the instructions you are looking for would be. Maybe someone else would know.
I learned from looking on a BBcode site. I just searched on BBcode and got several sites that explained how to do things in BBcode.
What is it you want to link to? Maybe if you provide the url you want to use, we can show you exactly how to format the command. Yes, the easiest thing to do is to go to the page you want to link to, then go up to the address bar and copy and paste the address.
Also be aware that on the forum we use BBcode and not HTML, so depending where you wanted to do this linking, it might not work if you use BBcode. If you want to do it on a blog, say, the BBcode tags would not work.