Nodes are locations on the map that can be connected for usage with workers and trading. You must find the corresponding node manager and talk to them to discover the node and even if you discover without talking to them, I suggest to do so to try and make sure you get credit for the find.
You don't need to invest in the node for it to count.
Find 30 and the achievement is yours. Should be plenty in the first camp area to Velia, and down towards Heidel.
This is a map for the PC version, so there is more than offered in the Xbox version, but you can view nodes and other information here.
The red boxes include different pass through nodes, such as connection, gateway, or dangerous nodes. http://www.somethinglovely.net/bdo/