Organizing food reserves for your base is the second important thing after sustained oxygen production. There are only a couple of food sources in the early game. You can harvest wild plants/grow your own or hunt critters. Wild plants don’t need water or care, but they grow much slower than their domesticated versions.
Daily consumption of one duplicant about 1000 kcal. Starving eventually will kill your dupes, though they can survive a couple of cycles without any food. Quality of food can change morale bonus of its consumers. Obvious that barbeque (Superb quality [+5]) tastes better than raw meat (Grisly [-1]) and has higher morale bonus (+16 vs -1). But better food requires more work and time to prepare.
Almost all foods need to be properly stored or it will spoil over time. Exceptions are Muckroot, Berry Sludge and Nutrient Bars – they never rot. You can use Ration Boxes or the Refrigerator. Sterile atmosphere will protect your food from deterioration, but this approach requires some engineering skills. It's also better to have food storage close to your farms/consumers to prevent long running distances.
Each plant requires its own range of temperature, beyond which it doesn't grow. In early game create farms in locations that already have good conditions and temperature.
Getting food at the beginning.
Despite that you start the game with some reserves (16000 kcal of Nutrient Bars), you will have to start searching for food as fast as you can. Search for growing Muckroot, Mealwood or Bristle Blossom around the base. Just enable autoharvest on plant and your dupes will collect all future harvests.
Until you researched base farming, don't dig out any plants. Just gather what you need and they will regrow soon.
Build Microbe Musher. It's able to produce Mush Bars (Grisly quality [-1]) from water and dirt. Major disadvantage is that Mush Bars always contaminated with small amounts of food poisoning germs and may cause diarrhea if not stored in chlorine. However, often this will be the only solution during famine or when waiting for harvests. Keep in mind that Mush Bars are disastrously inefficient for regular food production. They consume extreme amounts of both dirt and precious clean water.
Advice: make sure that your dupes always wash their hands after toilet, dirt compost and before they take food. Protect water reservoirs from contamination, never build outhouses near clean water sources. This will help prevent the spread of germs around your base and help to avoid food poisoning in water.
After farming research your first homegrown plant will be Mealwood (10-30°C). 3 cycles to harvest, requires dirt as fertilizer, don't need water to grow. Roughly four Mealwoods can provide enough food for one dupe, though this number depends on farming skill. Preparing Meal lice to Liceloaf is preferable way to consume it as of the greater food quality and nutritional value.
Second way to obtain food is hunting critters, such as Hatch and Drecko for meat. Most of the time there are not enough of them to provide enough food.
The difference between Planter Box and Farming tile is that dupes can walk on the last like on other tiles. The Farming Tiles' plantation also can be upgraded with the specific fertilizer. Hydroponic tile provides automatic irrigation when connected with liquid pipes to water source. This will allow you to prevent dupes from running with water bottles.
Food sources at middle-game.
After you have exosuits and start digging into surrounding slime, it's time to plant Mushrooms (5-35°C). Create a pit for carbon dioxide and make your farm there. Despite Poor (+1) food quality of Fried Mushrooms, Dusk Caps need only 4kg of slime per cycle to grow. Use saved water in the electrolyzer. Or plant some Pincha Pepper and use Slicksters eating CO2 or Dreckos on a balm lily diet for unlimited meat and eggs source. Stone Hatch may be a good choice too – feed them with Igneous rock and collect extra coal for free.
In case you found cold steam geyser and have an unlimited water source – explore all recipes from the cook book and choose one that fits your game style.