The script sbin/start-yarn.sh does just that
# start resourceManager
"$bin"/yarn-daemon.sh --config $YARN_CONF_DIR start resourcemanager
# start nodeManager
"$bin"/yarn-daemons.sh --config $YARN_CONF_DIR start nodemanager
in the yarn-site.xml you can set the IP:PORT of the resourcemanager as well as the node manager
yarn.resourcemanager.address
yarn.nodemanager.address
The node manager is the one that locate the resource manager (see http://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-site/YARN.html)