Welcome from Southern California. If the picture is stored on your Computer you can hit the reply button, type in a few words explaining what you are posting then when you go to the bottom of the page, don't hit submit yet, hit the attach files button. scroll down and you will see another window you can write in again and the "browse" button. I go to where my pictures are and double click the picture you want to show. You can post up to 3 pictures. Now, unless you have resized them, it will take a few minutes to load. Let it sit, go get a cup of tea, or coffee or something. Do not hit the preview button, it will wipe out your pictures. When it is done loading it will go to your post and your picture(s) will be showing. If you want to add something to the smaller text box, you can hit the "edit" button and add whatever, as long as you do it within 20 min or so.
Hope this helps. I don't know how to resize pictures. Remember it takes a few minutes to load.