What is drone agent

I am new to drone. I follow docs to install drone on my local server, everything works fine. I also use vault share secrets between reps, and install the related extension https://github.com/drone/drone-vault . the extension docs say I need put some config to drone agent

Update your Drone agent configuration to include the plugin address and the shared secret.

DRONE_SECRET_ENDPOINT=...
DRONE_SECRET_SECRET=bea26a2221fd8090ea38720fc445eca6

The problem is I can’t find docker agent in docs.drone.io. please help me.
Is drone runner is replacement to drone agent ? But I can’t find similar config in drone runner reference

Is drone runner is replacement to drone agent

yes, they are synonyms

how to config DRONE_SECRET_ENDPOINT and
DRONE_SECRET_SECRET in runner , I can’t find related configuration. Or any alternative to use vault in drone