You need to download paint if you dont already have it, press screenshot, open paint and paste your picture there. Then you need to click File=>Save As and then call it whatever you want(make sure there is a .jpg at the end) and save it to a place that you will remember where it is. Then, open one of the photo sharing sites that you have registered on(I personally would recommend photobuckit but thats just me) and there should be an upload button, you need to click that and select the file from where you saved it. Then it should start uploading. Once it is done, you need to click on the photo that you have uploaded, and there should be a link leading to it. Once you have done that, you need to copy and paste the following code:
[img]image link[/img]
Then, you need to enter the link to the image in where the it says "image link" and tada. You should have your image uploaded. Does this help?
EDIT: Wow two people posted less than a minute before me, and this took a while.