Step 1: Find some seeds. The seeds you're going to need depend on the recipe you're going to make.
Step 2: Mine for some minerals. You're going to need the minerals to build water purifiers and stockpile on water.
Mining is simple. Use the mine verb to mine at a certain tile. After you have depleted the resource from that tile, mine vertically up for a better chance of a new mineral, or horizontally for a better chance of the same mineral.
The resources you need are: Stone, Copper, Coal and Titanium. Some minerals are harder to find than others, so don't be discouraged if it takes a bit of time.
Step 3: Once you have enough minerals for a water purifier, build one and start purifying sea water. Make sure to collect the water from your purifiers. If you are fast enough, you can purify up to 30 waters per water purifier.
Step 4: Once you have collected enough water from your water purifier/s, it's time to begin growing your crops.
Crops typically have three stages. They must be watered at every stage to ensure they do not become rotten and die. The minimum amount of water you must use for every stage to guarantee its growth is 6. It's still possible to grow with less than 6 however it is unadvised to do.
Example: Tomato crop (stage appearances differ based on crop type)
Stage 1 appearance:
Stage 2 appearance:
Stage 3 appearance:
Stage 4 appearance:
Step 5: Assuming you made it to stage 4 successfully, you are now able to harvest your crop. The more water you used to grow your crop, the higher the yield amount.
Step 6: Eat your grown food, or use it as a recipe to prepare other meals. Most recipes use a combination of different ingredients to make, so you must prepare all of them before hand. If you want to check out the recipes you can make, make a chopping board by collecting wood from a tree, or find a bench. There you can see all the various types of foods you can make.
As technology improves, the tools you use to mine becomes substantially better which makes finding minerals much easier. More minerals means more water, which means easier time growing crops.
Growing food is not for everyone. You can always find somebody to make you some food in exchange for something. Or with enough power and influence, for nothing really.
P.S Don't forget to cook any recipes you do make.
Good luck.