Metasploit in one of the Swiss army toys that can do a lot of things. Starting from network discovery with its inbuilt nmap scan feature up to searching for exploits, up to exploiting the target computer.

When we want to use Metasploit for the first time since you booted your system, in a console as root users, run:

msfdb init

Start up metasploit in a console:

msfconsole

The first thing you need to remember is that you can easily get help in the msfconsole by typing help. With the help feature you should get your way.

Search for some module, for example samba:

search <keyword>

Then use the module. You can type in the module name or the line number as argument for use:

use <module-name>

Look to what options you can / need to set:

show options

Look maybe also to the show advanced options:

Set the option. Use setg if you want to set it clobally.

set <some-option>

Execute the exploit:

run

See here for a more complete walk through: https://github.com/dvanmosselbeen/dvm-docs/blob/master/OS/Security/metasploit.md