It doesn’t have to be long, and there’s no obligation on what to say. Some folk may be more-or-less anonymous, others may want to say more about themselves.
Some folk like to share identity labels, type of plurality/plural labels, size of their system & whether or not they’re polyfragmented, how long they’ve known they’re plural, maybe a few names of folk in their system likely to participate in the course, where they’re located in general or time zone type stuff for context, and maybe why they’re here or their attitude/hope for the course — that’s all optional.
It’s nice to have an idea of who is in the course for context’s sake.