Well, what SheWulph has provided are sufficient, I'll post an explanaition of my own:
First off, you need a site that you can upload your pictures, if you plan to use your own (If not, skip these next two paragraphs.). Many people use
PhotoBucket, but any publicly accessable place (somewhere you don't need another screenname to get into) will do (I use my own website.).
Once you have an account/site, start uploading your pictures. I don't know how to with PhotoBucket, but there should be some help manual type things somewhere around there.
After all your pictures have been uploaded (Onto a regular site, not PhotoBucket), right click the desired picture. There should be a tool bar that pops up. Find "Properties." A box should come up that has the properties, and there should be an area that says on the left "Adress [URL]". To the right there should be URL. Highlight it and copy.
Once you have that done, go to your post. Either type "[IMG][/IMG] and paste the URL in between the two, or go to the toolbar at the top. Find the button on the second row that says "IMG." Click it. A box should come up telling you to enter the complete URL for the image. Paste the URL you copied. Make sure to take out the first "http://"! If you don't, the picture will not show up correctly.
If your using PhotoBucket, once your pictures have been uploaded there should be three boxes with text. To the left, there should be three captions that say: "URL", "Tag", and "IMG". Highlight and cut/copy the text out of the "IMG" box, and paste it onto your post.
Preview your post and see if your picture shows up. If it doesn't, then you've done something wrong. If the URL shows up with the [IMG][/IMG] tags showing, then you probably mistyped one of the tags. If the picture shows up with an "X" and "User Posted Image," then the URL is probably typed wrong.
Hope this helps!