Depends what you want!
1) If you want to post a link to a web-site, this works:
Copy (highlight and right-click and hit copy) the url, (that's the gobblygook stuff in the top of the page you want to link to), and post it into the body of the post you want. It sometimes helps to have 2 instances of your browser open (Internet Explorer, Firefox, Safari, etc.), to work with both pages. One you want to copy from, and one you want to paste to.
Like this. http://ffn.yuku.com/topic/20642#.VSQiBzeVvRY You may enjoy that thread, by the way. :)
2) For copying text:
A. Copy (left click and highlight the text, and right click, (depends on what you are using, I use a mouse), hit copy, then go to the body of the post on the site you want to post it in, left click in it, then right click and hit paste. Now, if you are using a phone, tablet or a laptop, you will need to ask for directions, from the people that use the same kind of device as you. We all do it so, I'm sure someone will help you with the particular kind of device you use. *You may even want to elaborate your circumstances more, in another thread on the Main Board here, so people using similar devices, can help with the kind of device you have.
B. You can copy the text in to a text editor, in your Operating System or from your files you have already, (like your journal above), then go to the site you want then, start a thread and post, and use the copy and paste method, from the text editor, or your file you have already.