The Developer Beginner trail on Trailhead walks you through the basics of the Salesforce platform before diving into the real meat of the platform; Apex.
Apex is a programming language developed by Salesforce that allows you to do pretty much anything you want within the Salesforce platform. It is very similar to Java.
The business process automation and low code customization of Salesoforce is powerful in its own right. But if you want to do things that are truly custom or unique to your organization then learning Apex is a must.
I have finally finished all of the sections that come before Apex and will spend the next few days learning the basics, learning about Triggers, and learning about Testing code in Apex.