Hello! And welcome to the wide world of cycling... and triathlons! I too got into cycling so I could compete in tri's!
OK. Let me ask... do you have a computer with cadence on it? If not, go get one. I honestly never understood my gears or how to be efficient on my bike... and not mash the pedals until I got a computer with cadence.
Basically, when you pedal, you want to keep your cadence around 90-95 (this is debateable... but most say this is a good cadence to keep). If your candence falls below 90, then you want to shift so it's easier to pedal (down) or if your cadence is above 95, you will want to shift so it's harder to pedal (up).
As far as riding alone... well, I find it boring too... so I don't do it. I always ride with groups.
Of course, keep in mind that in a triathlon, you ride alone. Sure, people are around you, but no drafting is allowed and you can't ride next to someone and chat with them.
Riding is fun... when you know how to pedal efficiently. You get to go fast and the wind blows on you to cool your body off. You get to see scenery, and you can find riding clubs to join so you don't have to do it alone.
AND... since you are a runner, you will be a strong cyclist, catching up to the fast people very quickly!
Now, get out there and RIDE!
PS- www.beginnertriathlete.com, is a great resource for triathlon information. You can also log all your workouts there, it's very cool.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"