Options (top right corner) -> Turn allow joins ON, make sure the password box is empty.
This will make it so anybody searching 'find a party' will be able to find you, under the party restrictions.
Party restrictions:
Must be in the same ascension tier.
Must be within a specific level range (unless players specifically search for your name).
There's also the ability to allow you're guild members to join you:
Social -> guild -> Manage -> Public join 'ON'
For this ^ you need a guild of course.
NOTE* This is for 'creating' a party, not joining one.
This will make it so anybody searching 'find a party' will be able to find you, under the party restrictions.
Party restrictions:
Must be in the same ascension tier.
Must be within a specific level range (unless players specifically search for your name).
There's also the ability to allow you're guild members to join you:
Social -> guild -> Manage -> Public join 'ON'
For this ^ you need a guild of course.
NOTE* This is for 'creating' a party, not joining one.