This solution doesn't show where to find every standing stone, but tells where to find the first and easiest ones.
After you leave the first dungeon from the main quest with the guard (Hodvar), follow him. He will walk outside down a path, after a while he will stand still at three stones. You cannot miss them. As soon as you leave the dungeon and complete the Unbound quest, it's marked north-west on your map from your location. It is the only mark you see north-west on your radar. Use your activate button on one of them and you will unlock the achievement. It doesn't matter which one you choose, you can always change the chosen stone later on in the game.
The stones represent star signs, at those three there is a warrior, wizard and thief. They give you bonuses by leveling faster some of your skills, or have special effects. There are more of these stones in Skyrim, but these are the easiest and earliest ones you can find and you can only have one stone active at a time. If you somehow missed this stone when you came out of the dungeon, go to riverwood, and walk back up the mountain, just follow the road, it's not far off the road, you can see the big lake from the stone platform.
You can see the stones on the map too if you've discovered them, the picture of a standing stones looks like the pillar you see on the achievement picture. If you haven't discovered the standing stone, it will be blacked out.
Also, some of the red crosses on your (real life) map you get with the game, mark these stones, but not all, some mark dungeons or word walls.
There are even some books, if you read them, a stone will be marked on your map