As a SharePoint admin or Office365 admin go to https://{tenantname} Replace {tenantname} by your tenant, without using curly brackets.

In the classic admin center (not new preview one)

  1. Select New
  2. Select Personal Site collections
  3. Fill out the form. We advice the use of /sites as the managed path. Choose Team site (classic experience) as the template to be used. Select Ok to create the site collection.