Once you've registered your hosts in SSH Professional, you can distribute client access instructions to your end users, which will guide them through installing and configuring Step SSH.
Client/End User setup of Step for SSH is trivial. From your Dashboard, under SSH Professional's configuration page, there's a hyperlink you can send to end users (e.g., clients), which has your team name already configured.
Optionally you can share the following client quickstart link, using your team name as a parameter value.
https://smallstep.com/app/teams/quickstart?team=[your_team_name]