CiviCRM with WordPress or Drupal: how does the integration work?
CiviCRM can run alongside both WordPress and Drupal.
In either case, CiviCRM remains the CRM. It stores contacts, memberships, events, contributions, activities, relationships and other constituent data.
Where the two platforms differ is in how that data becomes part of the wider website.
For a relatively simple site, the difference may not matter very much. If you mainly need CiviCRM for event registration, donations or membership administration, both platforms can provide the website around it.