Hi Jamesmac and WilliamMcClellan,
If you have never recorded yourself on your computer before then I recommend doing that before trying to jam online.
If you can get a good recording using a program like Audacity, Reaper, or GarageBand then jamming with others will be easier. There is a lot of information online about how to record various instruments and get good quality audio (including YouTube videos). Feel free to let me know if you need help with that.
The first steps to getting familiar with jammr are:
1. Read the overview of the user interface to find out what the buttons do:
https://forum.jammr.net/topic/1727/2. Read the instructions for having a successful jam:
https://forum.jammr.net/topic/1724/I hope these pointers will get you jamming with us!