There are two approaches you could take with this, both start with creating a keyword for logging into your application
- Call a login keyword as the first step in each test or with a Test Setup, close the browser as the last step or with the teardown.
- use Suite Setup to call the keyword that opens the browser and logs in then, use Suite Teardown to close the browser. If you choose this method ensure all test cases assume you could be anywhere in the application, for applications with a global navigation menu or for api testing this is not really an issue, just be aware of it and how it applies to your application.
There is no right or wrong way, it depends on what works best for your app, I have used both approaches.
Hope this helps,