In order to mount NAS unit / network folder in linux / Raspbery PI place this in your /etc/fstab

//  /mnt/mymount       cifs   uid=1000,gid=1000,rw,username=myusername,password=MyPAssWD      0       0

# or if you use older samba version

//  /mnt/mymount       cifs   uid=1000,gid=1000,vers=1.0,rw,username=myusername,password=MyPAssWD      0       0

Now in order for Rasp PI to mount this on boot you need to configure in sudo raspi-config

Boot Options > Wait for Network at Boot > Yes