For this achievement, you'll need an pickaxe, that you can get from a miner outside the Orphanage, to the north. Thanks to the pickaxe you will be able to mine rocks.
If you aim to get this achievement as soon as possible, you can go to Palmaya on the west of the Orphanage, with a ferry. On the south-west of the city, a girl will have a quest for you: get her a launch from the restaurant. After that, she will create Nexotrap for you, if you have the materials: 3 rocks of a same element.
You can also craft Nexotraps on Drake isles, on the right of the healing center.