"Jamulus How to" by Anand Sitaram is a very good introduction on how to use Jamulus. If you don't have time for the full hour, we recommend you at least watch the 23 minutes between 09:20-32:20. At 46:43, Anand and Jonathan talk about building a specific Jamulus computer on a Raspberry Pi, which is part of the solution we offer at MusicBridge.
For singing online, a good quality USB headset works well. We recommend the SADES USB gaming headsets.
For instruments like pianos, cellos and violins, a condensor microphone is a good choice. In this case you will also need to connect stereo headphones to the microphone itself.
For electric instruments such as electric keyboards, synthesizers, electric guitar, or electric bass, a USB audio interface is required.
In this case you will also need a microphone and headphones.