How to use salt if I am sending hashed password? If have application that is sending username and hashed password to server for authentication, how would I use salt for this scenario ?
Ask the server for the salt for a specific username. 
Compute the expensive salted hash on the client, send to server
Server performs a cheap unsalted hash(or HMAC) on the hash received from the client and compares with the stored value


Note that sending a hashed password doesn't mean you can use an insecure transport. You still need proper transport security, such as SSL/TLS/HTTPS or a specialized password verification protocol such as SRP.