Hey there, Opal! Usually what I do is have several tabs open in my browser. One is the new thread I'm starting, and then any others I want to quote each have their own tabs. Just makes it easier. Then...
I find the thread or post I want to make a link for, and then click on the URL in the address bar. You can either link the whole thread or just the one specific post. If it's a specific post you want to link to, you can click on the little Post # link in the upper right of the post itself (#1, #64, etc.) and that will open up the post to view singly without the rest of the thread, and you copy that URL. In the URL it will include either "showthread" or "showpost" (see the URL to know what I mean). I usually like to get the URL for the individual post and then I change just one word in the link from "showpost" to "showthread" and keep the "postcount=1" (or whatever the digit is) so that the link goes to a specific post but the reader can still scroll up or down in the thread.
Then in the new thread, you paste the URL in your post and highlight it, then click on the "insert link" button above and a little pop-up box will come up and you paste the link in there, too. This might be different in different browsers, but that's how I do it.
As far as quoting, and multi-quoting, from several threads, here's how. When you do the multiquote thing by clicking on the + signs in one or several threads and then go to your new thread and hit "Post Reply." Underneath the Reply box where you input your text, you will see a sentence: "You have selected __ posts that are not part of this thread. Quote these posts as well, or deselect these posts." It gives you a link for each (selecting or deselecting). If you click to select all those other quotes, it will automatically put them in your reply box.
I hope my explanations were clear. :/