There are hundreds of how to'a on making a grab my button widget posted on line. I thought about making my own, but there are so many wonderful ones out there. I want to take a moment to explain somethings that will allow you to better understand these tutorials.
First I want to tell you that you must have a 125 x 125 image. That converts to .208 inches by .208 inches. You can use a square avatar that you use for Facebook, etsy or any other site. All of my stores include an avatar for you to use. I recommend on this to use a business avatar and NOT a photo of you. This is a mini advertisement. Here are some photo editing programs that you might find useful if you need to create something.
Picasa - Free photo editing software from Google #1 in my book.
You must host this avatar or image in an online album. That is the link that you need to post in the grab my button code. I am a huge deliver is gmail. I love gmail. If you have a gmail account and you look at the top of your page in your menu you will see the following.
gmail......calendar.....documents......photos. I recommend storing your image in photos.
If you don't have a gmail account there are several online photo storage company's that operate for free. such as flicker or snapfish.
If you need help designing an avatar or blog you can always see me on my etsy shop. http://www.etsy.com/shop/VampireCraftin
If you want your own you can try one of these free photo editing software pograms.
Here is a tutorial I think you will find helpful on making the grab my button code.
This one is the easyist. http://www.mycoolrealm.com/sandbox/gbgen/
This one is also easy. I recommend..so you can become familiar with the process.
When the above sites ask for Your website/blog URL: they mean your website address.
When the above sites ask for Your image URL: they mean what is the link where your image is located. Almost all online albums have a button that says link this image....and they you will be given a code.
I hope this was helpful.