So, I guess you want to make your photos large, edlarge.
If you have a large photo on Bucket, right click it and copy the properties which will determine that size as well as its location.
In the post you want it in, click the gold picture frame in the line of B I U (bold, italic, underline) and all the icons on top of the box you're typing in. When a little window pops up, insert the properties there by right clicking and selecting 'paste'. Click in the white part of the line, and it will automatically delete the HTML in blue that's already there.
When you click the 'submit reply' button, the photo will appear in your new post.