Know that Greenreach Priory is the tutorial area of the game, and currently it is forced upon the player (you must complete the quest given by Brother Anselem to be able to reach Stonehill). The other catch is that once you leave, you cannot return - party members are also unable to join you in the instance of this zone (you can't receive help).
After the loading screen clicks off, you'll be thrown straight into the game. To your right will be standing a priest NPC named Brother Anselem who has a large yellow exclamation mark above his head. This tells you that he has a quest available for you. Speak to him, read (or skip) the dialogue, then accept the quest.
Help A Brother Out![edit]
"Please, can you help a man of the cloth?
We were settling into breakfast this morning, when the flagstones started quaking, and the dead began to rise from beneath! My brothers and I fled the Vestry, and when we peered through the windows, we saw those miserable undead drinking all the sacramental wine! They're shambling around as drunk as lords, and we're unable to return - please, drive them out!"
- Objective: "Rout the inebriated undead from Greenreach Priory."
You will receive: a key, choice of gloves. 350XP, 20C.
Head into the vestry and work your way to the boss. Since the church, like almost every dungeon, is randomized, the first room you enter may contain the boss. If you do clear out the entire dungeon, you'll be both wealthier and closer to a level up. When you've finished slaying the Hollow Overseer (the enlarged hollow arcanist with a glow around him) and as many monsters as you like, head back outside and talk to Brother Anselem again to get your reward.
"Thank the light, you've run those drunken horrors off! You have our thanks, <Player name>! You say a strange pale man was behind it all? Some of our parishioners have heard tales of such folk... I knew we could depend on you to investigate. I have another favor to ask of you - please return when you are ready to venture to Stonehill."
Take Letter to Captain Damon[edit]
"Again, you have our thanks for running off those shambling horrors. Are you ready to venture to Stonehill?
You could do met yet another service by taking this letter to Captain Damon in Stonehill. It's a plea for assistance to help investigate the appearance of the pale man, and this undead menace. To reach Stonehill, head west until you see Brother Merrim."
- Objective: "Take Brother Anselem's Letter for help to Captain Damon in Stonehill."
You will receive: 423XP, 23C, choice of belt.
The path to Stonehill will open up, so head to the west side of the priory (next to Brother Merrim marked by the first aid symbol on your minimap) to exit and go forth towards Stonehill. You'll reach the "Path to Stonehill" - a small outdoor instance that has two exits: Greenreach Priory and Stonehill. Once you reach Stonehill, you cannot return to the priory!