The first step might actually be a non-starter for most people. Notion is free, SharePoint is usually offered as a capability within a business or school's Office 365 subscription. I believe you can either subscribe yourself for $5.00 / month using this link:
https://www.microsoft.com/en-us/microsoft-365/sharepoint/com..., or maybe you're lucky and already have an account with your school / work. If neither of these work for you, you can also sign up for the Microsoft Developer Program, which is actually pretty cool; here is a guide for setting up a SharePoint site through the developer program:
https://www.sharepointdiary.com/2021/05/how-to-create-sharep...I should take a moment to clarify that I'm not affiliated with Microsoft or any of the links I'm posting here in any way. I make a living building web sites and as mentioned above, many of them leverage SharePoint. I find it a pretty easy way to build intranet solutions for my customers.
Assuming you've got your SharePoint site created within SharePoint Online, creating a "List" is pretty simple. Here's an article from Microsoft explaining how to do so:
https://support.microsoft.com/en-us/office/create-a-list-0d3.... Think of a list as a database table. From there you can create various types of columns including "look-up" columns, which are basically joining to another table on the same site with a foreign key.
I think from there you could dive into the Power Platform, but there's so much out there, I think this would be a good start.