Make new SharePoint share

Go to the Office 365 admin center (https://admin.microsoft.com)

On the bottom left, under Admin centers, click on SharePoint

Go to Sites -> Active sites

Click on Create, select Team site, select the Standard team template, click on Use template. Then, give the site a name and owner. Finally, click on create site. You can then add members.

You can add owners, members and admins in the SharePoint admin Active sites page.

To add external users, follow these instructions:

Click on View site

When you are in the site, click on the gear in the top right corner of the page, and click on Site permissions

Click on Add members -> Share site only and then enter the e-mail of the user

You should then be able to change the permissions for the users