This is just a little help to get you started with your first SharePoint site.
First things first, log into your Microsoft Office 365 Admin portal account at this link: https://portal.microsoftonline.com/admin/default.aspx
Use your username and password to access your Office 365 Administrative portal site. If you have trouble logging in, use the forgot password option to reset. Once successfully logged in, select the drop down menu under Admin and select SharePoint. The next page that loads will be to administer your Sharepoint site information. Once loaded, you will be managing your site collections
as Microsoft refers. Think of this as the master and root destination to manage everything.
If you already have a few URLs listed, like, https://domainname.sharepoint.com
then you are well on your way.
Want to create/check ownership of that domain created? Select the domain in question and on there is a tab above that has a drop down entitled "Owners, " click it and choose Manage Administrators. From here, you can check who is your primary site collection administrator as well as see who is your site collections administrator(s). In the event you want others to share the task of editing or managing the site collection with you, adding administrators will be the next task.
Simply do the following:
Select the URL you want to add administrator(s) to, then hit the same button you did before, Owners. Once that is selected, you will again see the primary site collection administrator and the box below will give you the option to add and remove secondary administrators to the site. You can use the address book selection to search users within your domain or you can add a support personnel from this option which is outside of your domain.
Although none of this is simple, I hope over time becoming familiar with the operation of hosted SharePoint will be a lot easier. Hope this helps get you started with a very basic task in SharePoint.