Metasploit is a vast framework. When you say how do I use it, you first have to know what you want to use it for. So, what do you want to use it for?

metasploit has many uses bro i can't write everything here but in the link below u can get a starter guide so check it out. if you have anything regarding to the tool search for it or ask me am here https://www.tutorialspoint.com/metasploit/index.htm