Hello there!
Walk us through what you've done thus far, and what your end goal is. It's hard to understand when we aren't viewing the problem with you.
So, I'm going to take my best guess, and you can tell me if I'm right or not. You were in game, you took screenshots of your Dynasty, you exited the game. You got on the forum and started a topic wherein you went to your screenshot folder (found in My Documents>Electronic Arts>The Sims 3>Screenshots) and attempted to copy and paste them into the forum. Correct?
If this is the case you cannot just copy and paste pictures into forums as they require 3rd party hosting site to put them on the internet and make the translation (of the pixels on your computer harddrive to that of the internet). So what you'll want to do is sign up with a 3rd party website that hosts pictures (things like Photobucket, Mediafire, etc) and when you upload the pictures you'll want the "Direct Link" which you'll paste into the brackets that say [img ]http://directlinkofphoto[/ img] (I have spaces placed in my version so it is able to be viewed rather than assuming I'm trying to post an image). This is how you are able to view images on the forum.
Let me know if I was right or wrong or if you need clarification on anything.
Edit to add a more specific example. This is from my Life States Dynasty.
I use Mediafire.com, I go there and upload my picture then I right click the picture and click the option to "Copy Image URL."
This will give me this when I paste it into the forum:
http://www.mediafire.com/convkey/4df6/o1usapqf9ea77s9fg.jpgWhat I do then, is I hit a button on the forum that says "Images" or I type in [img ] (without the space between the bracket)
http://www.mediafire.com/convkey/4df6/o1usapqf9ea77s9fg.jpg [ /img] (without the space between the bracket or the link).
So it will look like this:
for other people but like this (minus spacing in the img and brackets) for me when editing:
[img ]
http://www.mediafire.com/convkey/4df6/o1usapqf9ea77s9fg.jpg [ /img]