Make a couple stacks of sticks. Place four sticks in the crafting grid, on the sides and one above the other. X is a stick and O is empty:
OOO
XOX
XOX
You'll want at least a stack of crops. Crops can only be placed on tilled soil, which needs water within four squares. Each crop can contain one of any vanilla plant except cactus, though it takes four for both flowers. The plants take a bit of time to mature. Right clicking on a plant harvests the crop while leaving the base plant behind. It gets dye from the flowers. Left clicking gets the resource and sometimes (often for vanilla plants) a seedbag that can only be planted on crops, while destroying the plant.
Wheat plants can be havested (right click) for wheat while leaving the plant behind. No seeds that way, but the MFR Harvester can harvest the wheat without destroying the plant, so no need for a Planter.
Placing a crop on an empty crop is used for crossbreeding. Note that an empty crop, including a crossbreeder, will eventually sprout weeds in it. They look like three dark green sprouts from the side. Weeds spread to other crops, destroying the original plant. So left click them whenever they appear.
Crossbreeding requires two crops with plants on at least two of the sides of the crossbreeder. It usually produces one of the parent plants, but sometimes a different plant. It's mostly random, though different plants are more likely to be produced from certain parents. You can sometimes get melons and pumpkins this way, or even nether wart. There are also IC2 specific plants, though too many to describe them all. There are a couple different colored flowers, including black. And reeds sometimes produce what looks like a reed with brown spots on it called stickweed. Which is harvested once for IC@ resin and a second time, though this makes it take longer to grow back, for reeds.
You don't need much space to crossbreed. But you have to keep monitoring them to watch for weeds, and they take time to grow. But for just harvesting you don't need to monitor them, just plant them somewhat quickly.