The wealth of DM advice available online today is a mixed blessing. Yes, it's nice to draw on the experience of dozens of long-time DMs, or watch personalities like Matt Colville, Matt Mercer, and Chris Perkins do their thing.
However, all that advice has fostered unrealistically high expectations of the role of a DM. It takes years to become a skilled and confident DM. You have to start small - both in scope and in expectations. All of those famous DMs started with dungeons that afforded only narrow range of actions. They didn't create whole societies, plot world-shaping plotlines, and write up deep backstories for every NPC. Not until they had been DMing for years. They started with Keep on the Borderlands, the Village of Hommlet, and other small-scale dungeon adventures.
So start with a small village or inn with a couple NPCs. A ruined temple or fort with six or seven encounters. PCs who are travelling explorers or tomb-raiders. This is a manageable scope of play for novice DMs.
And it's conventional advice to use published materials when you start. But many adventures today are 36+ pages of walls of text with an enormous amount of background and details to learn - much of which is unlikely to ever come up in actual play at the table. The advantage of creating your own material is you can A) make it very small and manageable in scope, and B) you won't have trouble memorizing it.