how i do i get to nepal from china?

You can buy an airline ticket from any airline which offers flights to nepal. Srilankan is the most economical, but there are other airlines like Airasia, Malaysian, Emirates.

Once you decide on your airline, you can:
1. Use a credit card to purchase the ticket online.
2. Purchase tickets through a travel agent.
3. Call the airline's office in china, send them a mail with the dates you want to travel pluse your details, and then make a bank transfer(they will tell you what to do over phone and via email).

I don't know if any trains go directly to nepal. It is very far and it would be an awfully long journey. You could take a train to sichuan, and from there take a flight to nepal? Or guangzhou.