Welcome to Photography Review.

You can post either in the Gallery or in each individual thread. The link that Frog provided is a good start.

When you begin a New Thread, by scrolling down, there is a box labled Additional Options which has an Upload button. Then just follow through (as in Frog's post) to add a new image.

If you post in the Gallery, there is also an Upload command and then you can link photos directly from the Galleries here to you post.

Good luck!