Anyone can use PicMonkey
Unfortunately, I cannot screenshot in the editor of Picmonkey, so I'll just TELL you what to do. Click here for a text tutorial.
Step 2: Add overlays
To add overlays, simply click on the butterfly icon in the menu. If your canvas is white (You can change the canvas color under the magic wand icon), it goes with most overlays. All of Picmonkey's overlays are compatible with any color, but if you would like to add your own overlays, I would suggest going with white. Anyway, to add your own overlays, search on the web for anything.png If you would like an overlay that is compatible with any backround color, search for one word and then "transparent". This looks for images that are placed on a transparent canvas. To check for this, select the image. If you see a white and gray (or grey?) canvas behind the image, it's transparent. For example, here is an edit I made very recently.
First, I downloaded these free watercolors off the web.
Step 3: Open Google Docs and start writing!
What else is there to say? Have fun!