Taking over our Sharepoint and overwhelmed. Where to start?

Skrutsch 

In addition to the solid advice already offered, here are a few more things to consider...

First of all, a quick note on what you should avoid modifying until you get a really good handle on things: Permissions. Permissions can get very tricky, and a simple click or two can cause some drastic changes with regard to who can access what. You might remove an individual's access to a document, or you might lock a lot of people out of a site. You can even lock yourself out. So be very careful with permissions.

• https://docs.microsoft.com/en-us/sharepoint/sites/user-permissions-and-permission-levels
• https://docs.microsoft.com/en-us/sharepoint/modern-experience-sharing-permissions

You'll probably want to read up on the differences between "classic" and "modern" SharePoint. Here's a good place to start with that: https://support.microsoft.com/en-us/office/sharepoint-classic-and-modern-experiences-5725c103-505d-4a6e-9350-300d3ec7d73f

https://docs.microsoft.com/en-us/sharepoint/information-architecture-modern-experience

You might consider creating a SharePoint sandbox (test environment) to "play" in. https://support.microsoft.com/en-us/office/create-a-site-in-sharepoint-4d1e11bf-8ddc-499d-b889-2b48d10b1ce8, https://support.microsoft.com/en-us/office/create-and-use-modern-pages-on-a-sharepoint-site-b3d46deb-27a6-4b1e-87b8-df851e503dec and https://support.microsoft.com/en-us/office/using-web-parts-on-sharepoint-pages-336e8e92-3e2d-4298-ae01-d404bbe751e0. Learn about https://support.microsoft.com/en-us/office/move-to-the-modern-list-and-library-experience-2d5206c8-6154-4262-be28-9f97596d3875, https://support.microsoft.com/en-us/office/create-change-or-delete-a-view-of-a-list-or-library-27ae65b8-bc5b-4949-b29b-4ee87144a9c9, and https://support.microsoft.com/en-us/office/create-a-column-in-a-list-or-library-2b0361ae-1bd3-41a3-8329-269e5f81cfa2. SharePoint runs deep.

It's a bit of a tall order to be asked to take over SharePoint without having experience. Ideally, your company will pay for you to take training. To give it some perspective, people have entire careers working in specific areas of SharePoint. It's big.

Lastly, you'll find lots of SharePoint resources here: https://365trainingportal.com/sharepoint/

Good luck!