There are plenty of guys on here that will assist with motor works. Learn how to post photos for said guys to look at. Get a workshop manual relevant to your bike. Study the Yamaha parts catalogue ( online, its free ) relevant to your bike. It shows every part and what order it goes together.
Find a mechanic that will let you pull the motor down and then explain to you what is wrong with it and also explain how it goes back together by watching him. Take notes of what he says. You will not learn everything overnight but you will build up your motor skills quickly. Buy your parts from this guy ( not cheap arse supposed bargains from China ) This is your best option in my opinion.
Or if money is no option take it to a mechanic and say fix the fukn thing, I'm off to the pub.