SharePoint Online offers the capability to add external users to your site. An external user is a user outside of your organization. This blog post will explain step by step how to achieve this functionality.
First of all you need to allow the function External Users for the site collections. This is done for the whole tentant (Liljekvist.onmicrosoft.com) and adds the option for each site collection to turn on or off the feature of external users.
Click on Settings --> Manage External Users under SharePoint Online administration center.
Choose Allow and click Save.
SharePoint Online offers you the functionality to share a site, so when structuring your information it is important to have in mind that you cannot only share a document library or a document but the whole site.
Next step is to choose the site collection that we want to invite our external users to. With administrative rights, go to Site Actions and then Site Settings.
Click Site collection features under Site Collection Administration.
Click Activate on External user invitations.
Now you are ready to invite external users!
Go to Site Actions then Share Site.
Fill in the needed information for your external users and click Share.
Now you have shared your site with external users and are free to organize and group them accordingly to your preferences.