Marketing/sales has been the easiest part of the work to me, and I'm a "tech guy". You simply tell people about it and they'll throw money at you.
My first business was selling coffee. I put a coffee machine on a metal table, put some pallets around it. Some dude came and asked for an espresso. He said it was too small and tasted nasty. I told him I'd refund that and give him a latte, which was 8 times bigger than an "espresso". He refused and gave me money anyway. He was later a daily customer after the first latte though. More people came and we sold 100 cups on the first day. Did we do marketing? Yes, we told the people staring at us that we'd give them a full refund if they didn't like it. Nobody took the refund.
My first real startup was a recipe app with an ingredients store. People just went to the store and clicked "add to cart". I did not expect them to. We didn't have a dashboard for viewing orders (nor a cart, the purchase button just took their phone number and address). I hacked something that put together a cart on the dashboard, then I'd contact them on WhatsApp and give my bank account details (we didn't have a payment gateway either).
The hard part is often the product. If you have bad lattes, nobody's going to order another. If you don't have recipes for flaxseed flour, not that many people are going to order the flaxseed flour.
I'd say don't listen too hard to entrepreneurship gurus who tell you to "validate before writing a single line of code". Often the code is part of the validation. I tried to run ads for flaxseed flour and nobody bought it. There's a niche for it, and that niche was overadvertised by other sellers. Writing the code exposed us to a marketing flank we never knew existed, and the app was eventually acquired as a diet food marketing channel, because the CAC was lower than Facebook ads.
You can build something of value and give that for free. That's actually a little easier than trying to go the validation route. From there, you can use the feedback to pivot into something of higher value or is more monetizable (e.g. DLCs). Metallica didn't think they'd make money off music, so they started with t-shirts.