In my opinion, one of the easier ways to start growing things is to start with something like microgreens. They have a short grow cycle, don't take a lot of equipment or space, and can sell for a premium price.
What are microgreens?
If you haven't heard of them before, microgreens are the young plants of editable vegetables and herbs. Depending on the variety, they are generally ready to harvest within 10-14 days, when they have developed their first leaves, or cotyledon.
Since microgreens are harvested when the plants are so small, they end up being a lot more nutrient dense than their mature counterparts. Once harvested, they're great to use in salads, smoothies, sandwiches, stir fries, and more.
When it comes to light, having a south facing window that receives a lot of light throughout the day should work. You can also purchase some LED lights if you want to use a grow tent or don't have a suitable window.
Before planting your seeds, you'll want to prep your trays and potentially your seed. I typically use two trays for each set of microgreens that I'm growing. The bottom tray is solid and used to hold water, while the top one has holes in the bottom that allow the water to soak into the growing medium.
You'll want to fill the upper tray with medium (soil or hydroponic mats) and wet it, so it's damp but not soaked. Most seed can be planted directly, but there are a few varieties that need to be soaked first, such as sunflower, peas, beet, and wheatgrass. For seed that needs to be soaked, I've had luck letting it sit in a water/vinegar/hydrogen peroxide solution for about 10 minutes, and then overnight in plain water.
Once the trays are prepared, it's time to plant the seed. The amount depends on how large of a tray you're using and the variety of microgreens being planted. There are a lot of resources that tell you how much to use, but I've always referred to them as more of a starting point to see what works. A couple examples are Bootstrap Farmer and Johnny's seeds.
I generally pour the seed into a bowl that sits on a kitchen scale, and then sprinkle the seed over the tray. You want the seed to be fairly dense, but spaced far enough that they're not clumped up. Having too much can cause mold problems later on.
During the first few days, trays are left in the dark and stacked on top of one another. This allows the seed to sprout and roots to grow down into the medium. The duration of the stacking and blackout will depend on the variety being grown, but the Bootstrap Farmer sheet linked above gives a good place to start. After the blackout period, trays can be moved to a lit area or lights can be turned on.
Now that everything's been planted, we just need to add water so they grow. The first few days (before the seed has sprouted), I'll take a hose on the mist setting and spray down the trays. A spray bottle would also work well. After that, I start filling the bottom tray with water and allowing the soil to soak.
Try keeping the medium moist, but not to the point you get pooling. You don't want things to dry out, but you also don't want mildew and mold from watering too much.
Once the microgreens have grown 2-4 inches and developed their first leaves, they're ready to harvest. The simplest way is to grab a handful of the plants and take a pair of scissors to the stem, just above the soil. You want to be gentle as they're young plants and can easily bruise or get smashed. Another option is to use an electric knife or, if you're doing large volumes, a Quick-cut Greens Harvester.
Finally, once the microgreens have been cut, they're ready to store. A plastic Tupperware container seems to work well, but you want to make sure the microgreens are dry and not packed too tightly.
Storing them in the refrigerator should allow them to keep for about a week.