Need a memory refresh

[Linux for blind general discussion]

I am using Debian Buster, CLI  only. I have three users on the machine, besides the superuser. I can't remember the keystroke to switch from one user to another. 
ssh isn't really satisfactory, since it doesn't set up an independent user. Where can I find information like this?

Thanks,
John

-- 
John J. Boyer
Email: john.boyer at abilitiessoft.org
website: http://www.abilitiessoft.org
Status: Company dissolved but website and email addresses  live.
Location: Madison, Wisconsin, USA
Mission: developing assistive technology software and providing STEM services 
        that are available at no cost