..::4 Step Approach To Image Transparency::..

Step 1: First create your image [it is best to have your transparency a odd color that is not in your image]
Step 2: Press Shift+Ctrl+V*. Make sure Optimized Medium Cut has a little dot next to it, if it does click OK
Step 3: Now the Transparency Selection will come up. Hover over your image [an eyedropper icon will appear] and click on your background [which should be some far off color that isn't already used in the image], after
that click OK.
Step 4: Save your image as a gif and your all set.

*; You might get a dialog telling you that you need to have a merged image, meaning all your layers should be merged. Well you can ignore this dialog and just click OK [it will merge all layers for you]. Alternatively you can just check the box so that the dialog will never pop up or you can just merge the layers before you press Shift+Ctrl+V. Either way is fine.

Finished product: