Handlebar Bag

Hi

I have been looking at getting a handlebar bag, which can double for commuting and use on a tour. I have

been eyeing off the Ortlieb range of 5 and 6 plus bags. Couple of questions though.

I have been scratching my head on how they fit onto the bike, and do I need to buy an adaptor at the same

time. Is some one able to take a photo of their fitment, so it can help me out.

Also, what is the most common size to use, is better to have a smaller bag and carefully pack or the medium or large bag. Is there any tricks for steering.