Go to the management area of your ladder and click on the "Invite new players" link in the menu.  You will be able to email up to 20 people at a time adding a personal message inviting them to join your ladder.

They will be sent instructions on how to do so.  If you wish to instruct someone to find your ladder, tell them to search for the name of your ladder by clicking on the "Find a ladder" link in the menu.