I always felt this way back when 2.0 first came out and I started PLD (was mnk all through 1.0). Honestly your not going to feel comfortable until you get in there and try, learn, fail(there is no shame in failing, unless you choose to not learn from it), and finally succeed.

Gather a few friends and just explain exactly what you posted. "Can I get some help learning/clearing Garuda HM". Alternatively you can create PF stating that its a learning party and wipes will be expected.

The best advice I can give you is DO NOT be afraid to ask questions lol... if a mechanic happens and you do not understand it, ask what the appropriate method for dealing with it is. Also once you DO finally get out there and start tackling content you will start to feel more comfortable taking on new challenges as well.