It doesn't matter who installs Jenkins on a system. Generally you want to setup server programs like Jenkins (doesn't matter if it's master or a slave node) to run in the system context ( IE, as a service), as a local system user that's not you, and has the lowest privileges possible. I usually just create a local system account named Jenkins with minimal privileges.

The slave nodes are easy to setup but not totally straight forward. At a high level, each requires a unique key generated by the Jenkins master under Manage Jenkins -> Nodes, and the master has to be setup with the proper configuration settings to allow slaves to connect under Manage Jenkins -> Security -> Agents. Sorry I can't be more help on the slaves, it's been a long time since I set one up.