As a league creator, you have the option to make your league public or private.
Public - Public league creators and team owners can send their league URLs out in email (or post them on a message board) to have non-members view them. In public leagues, some pages (such as the list of team owners and the league message boards) are not viewable, but the main League Office, Standings, and Team pages are viewable.
Private - If you set your league as "Private" a password box will appear and you must enter a password of at least four characters. Only the league creator can give out the league password and/or send invites to join their private league.