OK, step by step. You've gotten the pictures from your camera to your computer, and you know where they're saved on the computer, correct? Your next step is to get to the "Reply to Topic" screen and look below the Reply window. The next box down is "Additional Options."
There are three "Miscellaneous Options" with checkboxes next to them, and below that you'll see "Attach Files" and a button labeled "Manage Attachments." Clicky.
This brings up a new window. If you've got a pop-up blocker installed, it may not let the new window come up, but you can set it to allow pop-ups from this site if you want.
In the new window, at the top, you'll see "Upload a File From Your Computer." There are three blank fields below that, and each has a button marked "Browse." Click one of those buttons.
That opens up your computer and lets you search for your picture. When you find the one you want, just double-click the filename and it will appear in the empty field in the "Upload a File From Your Computer" window. Then, if you want to upload other images, you can do the same with another Browse button.
When you've selected all the images you want, there's a button to the right of the Browse buttons marked "Upload Files." Clicking that actually sends the photos from your machine to the TFL servers.
If you've done it right so far, you can close the window and go back to your Post Reply screen. Your attached photos will be listed in the "Manage Attachments" box I mentioned before, and if you hit "Submit Reply" they'll be included in your post.
If the system tells you it can't load your photos because of the size, you will need to resize them using image software. Microsoft Paint can do it, but I like Paint Shop Pro from JASC, which is available as a free trial for download.