new here, i want my bike running like new.

[stonknod]

i bought a gz two years ago to learn on. i was the third owner i believe, the first being the dmv. i got my permit and learned to ride but only really the first summer i had it. as the weathers getting warmer i want to get it up and running again but i dont know where to start. i bought a new battery bc it needed one but the last time i drove it it wasnt running great. i dont want to take it anywhere and get ripped off bc i know nothing about bike, i would prefer to do work myself. im sure i need to change the oil and brakes. tires look good. there seems to be some oil or some kind of residue on the side of the motor in the little grilles. someone who apparently knows something said theres no leak but i'd like to have that checked out and cleaned up. also the exhaust pipes coming from the engine have discoloration on them thats like blue-ish? any help or advice would be greatly appreciated. also if anyone knows any links to places that sell replacement parts. after seeing posts on here i'd really like to add some things to my ride and replace some beat up parts. thanks.