This method allows you to reboot your Mac and have the mapped network drive automatically remount and appear on the desktop, this is more persistent than the above method:

From the Finder, hit Command+K

Enter the path to the network drive you want to map, ie: smb://networkcomputer/networkshare and click ‘Connect’

Enter your login credentials and click “OK”

The drive is now mounted, but continue on to map for system reboot persistence

Now enter into System Preferences, from the Apple menu

Click on ‘Accounts’

Click on “Login Items”

Click on the + button to add another login item

Locate the network drive you previously mounted and click “Add”

Exit out of System Preferences

Your network drive will now be mapped and automatically remounted when you reboot your Mac.

via Map a network drive on a Mac.