After you have talked to Adril Arano about Miraak, you need to investigate the Shrine.
Leave the Raven Rock Docks and follow the marker on your compass, it will take you to the Earth Stone Shrine, which is located a bit to the southwest of Raven Rock.
See the map below to help you get from Raven Rock to the Earth Stone Shrine:
Go to the Green Earth Stone in the center and Activate the Earth Stone.
You will have a vision. You will hear the voice of Miraak in your head:
"That you might remember...Your hands once were idle... And when the world shall see...Here in my shrine... Here do you toil... What faithless minds have stolen"
You will temporarily lose control of your character, and be brainwashed into picking the earth stone mindlessly with a pick hammer. Wait patiently.
Neloth, a Dark Elf NPC nearby, observes: "Fascinating. By touching the stone, you appear to have fallen under whatever influence is affecting the others". After the Earth Stone effect ends, Neloth tells you: "Ah, so you appear able to resist the effect by exerting your will. Fascinating!"
Speak to Neloth. He advises against touching the stone again. He asks what you are doing here. Tell him you are looking for someone named Miraak. He says it sounds familiar, but he can't quite place it. Finally he recalls. But what he has to say makes very little sense. Miraak's been dead for thousands of years. He is not sure what it means. Neloth cannot give you any answers, but there are ruins of an ancient temple of Miraak's toward the center of the island. and Neloth recommends looking there.
Before proceeding, feel free to talk to Neloth and get some more information.
Ask him what these people are doing. He says they are building something, clearly. And yet they don't seem to have much to say about it. Neloth is very interested to find out what happens when they finish.
If you ask him if he tried to stop this, he says that certainly not. Doing so would interfere with whatever is going on, and he would be unable to see how this all turns out.
This completes the following objectives:
Search for information about Miraak
Investigate the Shrine
Your next objective is to reach the Temple of Miraak.