If your business stops the moment you step away, you do not own a business, you own a demanding job. Systems are what change that, turning your knowledge into processes that run whether or not you are in the room.
A system is just a documented decision
Every time you decide how something should be done and write it down so it can be repeated, you have built a system. How leads are followed up, how clients are onboarded, how invoices go out, each of these can be a documented process instead of a thing that lives only in your head.
Document as you do the work
The trap is treating documentation as a separate project you will get to later. You never will. Instead, document in the flow of the work: record the task the next time you do it, write the steps as you go, and refine over time. A rough process today beats a perfect one that never gets written.
Hand the system to someone else
A documented process is what makes delegation safe. Instead of explaining a task from scratch every time, you hand over the system and let an assistant run it, improving it as they go. That is the difference between being busy and being scalable.
Build enough systems and the business starts to run on rails, freeing you to work on what is next instead of what is overdue.