Taking over our Sharepoint and overwhelmed. Where to start?

Skrutsch the number of members will only appear if the  it's a site created by a SharePoint Group. Don't worry about, for normal sites you won't see that.

To see the structure of your site the place you will go to most is Site Contents which you access from the gear icon at the top right of the site. That holds details of your document libraries (for storing documents unsurpringly), lists (lists of data which can also have attachments) and your site pages. You will also be able to click on the Subsites tab at the top of Site contents to see the subsites of your site. But you shouold be aware that Microsoft no longer recommends the use of subsites but have a more hub & spoke approach now where individual sites are "associated" with the top level hub site and take the same color scheme, can have the same top menu bar. We do this with our intranet where the hub site is the main intranet site, but we then have separate sites for HR, Finance, Legal, IT Support and so on. They are all associated to the main hub site. Apart from having common navigation and color there are other advantages; you can post news on one of the associated sites and have it appear in a news web part on the main site. And you can have news cascade down as well. And in my experience having associated sites makes permissions management easier than with subsites.

You should get familiar with the Site Settings page where a lot of the backend stuff happens. 

And when you are in a list or library, always go to the menu at the top right where you will see list settings or library settings as appropriate and can start to become familiar qwith what you can change.

And practice creating pages and news pages (they are not quite the same), adding web parts and seeing the options you have  for sections, columns.

I don't know why your sites wouldn't be showing xyz.sharepoint.com/sites/ then your site name as in Office 365 I thought every site on every tenant had this naming system. A screenshot my help.

I agree with thomasknebel that SharePoint can be difficult to get to grips with, but I find modern SharePoint far easier and more logical than the old SharePoint 2010 which I really do think was difficult. The way to learn SharePoint is exactly the same way as you would eat an elephant: one bite at a time. There are good videos on YouTube and you can always ask here. Some of us are on the site almost every day even if Microsoft are here far less regularly. Although we don't know everything (well I certainly don't!) where we can we will help with solutions, screenshots and suggestions. So always come back here and ask, we don't bite.

Rob
Los Gallardos
Intranet, SharePoint and Power Platform Manager (and classic 1967 Morris Traveller driver)