How do I know who participated in a meeting?

You can run an "Active hosts" report, it will show a list of active meetings and users during a specific time range, up to one month. Check Zoom's official article for Getting started with Zoom reporting for full details. You may try to access this report by following the steps down below:

Accessing reports in your Account:

1. Log in to the Zoom web portal.
2. Choose Analytics & Reports, if you are a member on the account. If you are an account admin/owner or have a role with the Usage Report permission, you will need to Account Management, and then Reports.
3. Select the kind of report that you would like (Active hosts). You can also click the User Activity Reports tab to view additional types of reports (only accessible to the account owner by default).