your question isn't completely clear to me. However, i will attempt to provide some initial guidance. First and foremost reference the Atlassian documentation as it is quite good and will do a much better job of educating you than i can here. If you follow the document I am sure you will be well versed in setting up an effective portal w/ the right users defined. Note the document link above is for cloud, if you are using server you can find it easily enough.
With that said, when you say "without having to use a user-license for JIRA" what do you mean? For JSD you have agents which are paid licenses and customers which do not add cost. Your agents work the issues submitted by your customers via the portal. You simply create a project, define the agents, define the customers and you have a basic setup...more or less.
glad you are up and running. Regarding ability to logout, I have never seen an instance of where a user could not logout. Simply click in upper-right corner where you avatar is and in the drop down select logout. There likely will be a secondary screen asking you to confirm logging out. With that said, I rarely logout as I am in the application pretty much constantly.
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