For the following explanation I assume that you have created a custom track in ~/.rally/benchmarks/tracks/all-my-custom-tracks and your track is called my-track.
To just run this track - say against Elasticsearch 5.5.0 - on your local machine you'd need to run:
esrally --track-repository=all-my-custom-tracks --track=my-track --distribution-version=5.5.0
If you want to run it against a remote machine or a cluster of multiple machines, use the --target-hosts parameter. E.g.:
esrally --track-repository=all-my-custom-tracks --track=my-track --pipeline=benchmark-only --target-hosts:10.17.23.11:9200,10.17.23.12:9200
You can find a complete walk-through in the docs.
Daniel