You'll need to have the content you want to feature in mind, and a photograph to represent each saved in your pictures folder. You'll also need to know how wide your sidebar is (blogger > template > customize > adjust widths > it will say your blog dimensions).
Go to picmonkey. Open up the first photo. If it needs any editing tweaks do those now.
picmonkey's main page and hover over design, click custom, and type in the desired dimensions. Use the same width as all of your mini photo buttons, and then for the height add up how tall they would be stacked together and tack on a few pixels so you have some room to work with.
Go to your photobucket and upload your perfected graphic. Copy the direct link.
image-maps.com and paste in your direct link in the designated box and then click 'start mapping'. When it loads click 'click to continue'.
If you have any questions please don't hesitate to ask me. I'm happy to help in any way I can. I'm definitely not a graphics or coding pro, but I do like being able to do my own blog tweaking and design.
Also check out my other how to posts: How to Create & Install a Blog Button and How to Create an Inspiration Board with Picmonkey.