Also, if you need a series title but have already published the strip, here's the easiest fix. Click "Comic" like you were going to create a new comic. Then click on the drop down box they mentioned below and put in your series title. Then just click back and choose "Yes" to leave the screen. Go back to the published comic, click "More Options" on the right, then click on the drop down box in the lower right hand corner, choose the new series title you just created, and click Move. It seems really involved when explaining it, but really, all it is is a few seconds of mass clicks.

When you are making a comic, at the top-left of the builder is a little grey bar saying 'Gerdie's Bitstrips'. Click on the arrow, and select 'New Series'. Then you're done.

you see the place were it says gerdie's bitstrips. click on the arow and go to new series