A first garden usually fails because it is too big: a full bed, several kinds of plants, and a season's wait to find out what went wrong. The way out is a first attempt that is small and fast.
Your first day
Buy a packet of radish seeds and, for a pot, a bag of potting mix, and plant in spring or fall since radishes bolt in summer heat. Pick a spot that gets at least six hours of direct sun a day, since radishes sulk in shade. Loosen the soil in a small patch, or in a pot at least half a foot deep with drainage holes. Poke holes about half an inch deep, two inches apart, and drop one radish seed per hole. Cover lightly with a pinch of soil and water gently, with a spray bottle or small jug, until the soil is evenly damp, not pooling. Look each day, but water by the soil: until sprouts appear, top up whenever the surface starts to dry, then water only once the top layer feels dry to the touch.
Most beginners overwater out of anxiety, checking constantly and adding a little more water just in case. Don't. Far more seeds rot from too much water sitting around the roots than ever die from too little.
The thing most people miss
Radishes are ready to harvest in under a month, so a complete result comes quickly and a mistake shows while it still matters, instead of after an entire season. That's the case for planting something fast and cheap to fail with before reading up on soil chemistry: the plant teaches you quicker than an article does.
A failed radish costs a few cents and a few weeks, and it tells you something specific about your light, your watering or your soil.
How you'll know it's working
Small green sprouts should push through the soil in nearly every spot you planted a seed, usually within about five days. Counting them against how many seeds actually went in is the real tell, not just that something came up.
Succession planting, staggering new seeds every couple of weeks instead of sowing one batch, is worth trying next, so the harvest doesn't all arrive in the same week.