Here's how it works for me. Go up the menu across the top of the home page. Look for a choice called "Uploads". Click on it. You'll get a page that, if you scroll down, has the option to browse your computer and find photos to upload. (I make sure that I've previously put the one or ones I want to upload at this time onto my desktop.) Okay, find the one you want to upload by name, then choose it. If it is too large a file for the SS system, click the little box that says "resize image?". Okay, once you've done that, then click "Submit". That uploads the file onto a personal gallery called "All My Uploads" - which SS provides for you.
Once you have an image (or more than one uploaded), you can place one or more images into your post. While you are writing a post, you can again click Uploads, and another tab opens in your browser, showing your image gallery. You'll see in the gallery of yours that there are two URLs for each of your images, listed underneath the individual image. You can copy either of these URLs (one for thumbnail, one for full-sized) and paste it into the post you are preparing. This will mean you then have at least two tabs open on your browser: one for the post you are writing and putting pics into, and one to see your upload gallery.
That's pretty much it. It may sound complicated before you've done it once, but after that you won't find it very complicated.