Here is how you can add new users to your SharePoint site. This walkthrough assumes you already created a user account in AD or in Office365.
Navigate to the site you’d like to share with the new user or a group.
If you need to share a homepage, then go to the URL of the homepage. If you need to share the HR landing site, then go to that site first.
Select Share site
In the Share site pane, enter the names of people or groups to add them to the site, or enter “Everyone except external users” to share the site with everyone in your organization.
You can change the permission level (Read, Edit, or Full Control) depending on what’s needed.
Click Share and your users will now have access to this site.
NOTE: If you have multiple sites in your tenant (HR Site, Business & Tools Site etc), you must repeat these steps 1-5 for all these sites so users have access to all of the sites you need them to be able to access.