While every Class will eventually have 3 Ascendancy Classes, Early Access currently has two for the Ranger. The Deadeye is your classic Ranger, specializing in Arrows/Bows and the like. The Pathfinder will have more utility with "Concoctions" and specialize in Poison.
Deadeye

The Deadeye is your classic Bow & Arrow character, shooting a variety of Arrow Skills to deal damage. The Deadeye also has access to Tailwind, a buff that makes your character much faster.
You can also choose to deal more damage by being up close, or by shooting from far away.
Pathfinder

[See Pathfinder Ascendancy Page]
The Pathfinder can also use a Bow and Arrow, but she has more access to a different type of damage skill with "Concoctions."
(Such as
Acidic Concoction)
You can pick the best Concoction to match your build (Poison, Lightning, Physical, etc).
The Pathfinder also has a very unique passive that gives you extra Passive Points on your regular Skill Tree.