To create a node, you first need to have a hub. If you don't have a hub, you can create it like this:
java -jar selenium-server-standalone-<version>.jar -role hub
Then you're able to create a node:
java -jar selenium-server-standalone-<version>.jar -role node -hub http://localhost:4444/grid/register // default port is 4444
More info here: https://github.com/SeleniumHQ/selenium/wiki/Grid2