Hello, Hendrick! Good to see that you've decided to make the jump from lurker to poster. Now.
Me personally, I use Imgur. But there are other sites you can use. Except Photobucket. Don't use it, because it's terrible, in the worst possible ways.
Once you register, you can upload photos to the image hosting site. In some cases, all you have to do is click and drag the image to that site, and it will figure out what you are trying to do, on it's own.
Once you have uploaded a photo, each site will have a slightly different way to access "share" links, but they are there. Copy the one that says it's for forums or bulletin board services, then paste that link into your post. Then, when you click the "post reply" button, the power of HTML will add the image to your post, where everybody can see it.
It's also possibly relevant to point out that you can ask about history, maker, tang stamp, country or origin, steel quality, or anything else you want, except for the value of the knife. Registered users (like you and me) can't ask about dollar values on the forum.
Hope that helps.