It took me a long time to work out the right size of image to get to fit my page. (Like an hour!) Hopefully if you want to do something like how mine is above, this will cut down on the time you have to spend to make it!
First upload your chosen image (the one you will have people click on to go to that tutorial) onto picnik.com (the editing you need is free for all of this, and even some touch ups if you want to do those too.).
Edit it first to make it pretty and then click on 'edit' on the top tab and then 'crop' on the left side menu.
I know, awesome freestyle arrow drawing skills.
Then select square. You can have it so it's not quite a square, but when you change the size later you may end up with a squashed image (I learned this the hard way...).
Crop your image and then select 'apply'.
Then click 'text' to add the name of your tutorial.
Choose the font, adjust the colour and size, move it around and then click 'apply' when you're done.
Next click 'resize' , I know you're blown away by my helpful arrows and circling!
Change the dimensions to 170 x 170 and click apply.
Then save to your computer and insert the image onto your tutorials page. Make it a link using this post.
You may need to adjust your size slightly to work for your blog, but mine is a standard width and it does three on a line easily.
Let me know if you have any questions. Or if you do it yourself. Or if you already knew how to do this and I'm just r e a l l y slow at picking this stuff up!
Enjoy your week!