Once you get used to your bike, you might find the D rides to be of interest.
http://www.ohbike.org/perl/rides.pl?month=07#class
Helmets do come in different sizes (small-medium-large). Different brands can fit differently on your head, so if you try one and it's not comfortable, you should try a different brand to see if it's better. For example Giro works for me, but others prefer Bell helmets.