andy
Which is the simplest method to backup my data ?
Simplest will mean different things to different people & will depend on your situation.
The basic supported default backup method is to use the server manager panel, backup or restore option.
Then configure a workstation backup, which includes the local connected USB drive option.
Typically set it to run at 2am every day & do a full backup weekly & incremental backups daily.
....and Stefano is correct, pls read the manual as I'm sure this is covered there, and much much more.