I've been using the buses to get into the mountains from Bangor for about 8 years now, and they can be pretty hard to understand. Padarn are here:
http://www.padarnbus.co.uk/Timetables.html
There are a few early morning direct buses from Bangor to Ogwen and beyond, but if you miss those you need to get a bus to Bethesda first. The 66, 67, 77, 76 and 7 will all get you there via slightly different routes and run quite freqeuntly. Get off at the Spar and the S6 can be caught from there. Another option is to get the bus to Bethesda and walk out to the end of town and try hitching. If you look like a walker/climber odds are someone will pick you up.
For the last two years Arriva have run summer buses direct from Bangor to Capel Curig and on to Pen y Pass and Llanberis. Hopefully they'll start again this year.
To get to the bus station from Bangor station walk out and the main road (Deniol Road) stretches down in a straight line. Follow it past the uni buildings until you find Marks and Spencers and the bus station. 15 minute walk maximum.
A final word of warning. Many bus timetables at stops are incorrect and out of date. It's best to believe what the online ones say. I've sent many complaints over the years about this and nothing ever seems to get done!