Bertie Bassit

Hello everyone, I'm Mike. I bought myself a westfield bass a few years ago, it was £50 new...don't laugh, it's a pink one lol but I'm not bothered about the colour, I've had established bass players playing it and they say it's not too bad for the money. Anyway I've started jamming with a few guys every week, we play mostly blue grass stuff and it's really just simple notes on the bass I'm playing. I'm wanting to ask two things, what is the best way to pick out bass lines in a song? I've downloaded a certain track from youtube and slowed it down with a program called Audacity, which is not bad for hearing how the bass line goes except that my ear is not proficient at picking out notes yet, so how can I identify the notes in a song. The other thing is apart from taking lessons, how can I progress to a more elaborate way of playing, i.e. doing fills and climbs etc, Is it just a case of going on line looking for lesson etc? Sorry to seem so dumb but I've never touched a bass in my life up till about 2 months ago, and am a complete novice, not a spring chicken either I'm 49 lol! I'd appreciate any help and advice, thanks