If you offer one-to-one or small group sessions and you’d like people to book online to save you doing the admin, you can do with plugins for Wordpress such as Bookly which offer a calendar interface where people can choose a time slot and pay for that slot You can set the time slot duration and what days you’re available.
Selling webinars and courses
You might have heard of Zoom, Microsoft Teams, and Google Meets especially since lockdown.
Zoom especially can be used to teach many people at once or just one-to-one. The screenshare feature is a great way for demonstrating software such as teaching WordPress, probably even better than via a projector in a face-to-face setting.
As with selling event tickets, you can use third party services such as EventBrite or Fatsoma to enable bookings and take payment. These services offer a way to limit places.
Bookley or the Events plugins to take bookings and process payments online via Stripe or PayPal.
We've used Bookly on a number of sites in the past, and their support is first rate!