Admin Portal Home: https://portal.office.com/adminportal/home
Under that, the different Admin Centers’ URL naming convention is in a quite mess.
Exchange is https://outlook.office365.com/ecp/?rfr=Admin_o365&exsvurl=1&mkt=en-US&Realm=yourcompanyname.onmicrosoft.com
Skype for Business is https://adminca1.online.lync.com/lscp/?language=en-US&tenantID=yourtenaneid
SharePoint is https://yourcompanyname-admin.sharepoint.com/
Under SharePoint, there is an OneDrive document repository for every user: https://yourcompanyname-my.sharepoint.com, it actually resolves to https://yourcompanyname-my.sharepoint.com/personal/yourname_yourcompanyname_onmicrosoft_com/_layouts/15/onedrive.aspx. Other than that, there are sites and teams, and the new stuff – groups.
Default site collection: https://yourcompanyname.sharepoint.com/
Video Portal: https://yourcompanyname.sharepoint.com/portals/hub
Community: https://yourcompanyname.sharepoint.com/portals/community
Search: https://yourcompanyname.sharepoint.com/search
Compliance Policy Center: https://yourcompanyname.sharepoint.com/sites/CompliancePolicyCenter
OneDrive is https://admin.onedrive.com/
PowerApps is https://admin.powerapps.com/
Flow is https://admin.flow.microsoft.com/
Security & Compliance is https://protection.office.com/
Azure AD is https://go.microsoft.com/fwlink/?linkid=849449