1. The difference between Timber and Wood and why it's important.
Woodcutting in this game works differently than the average sandbox. When you cut down a tree you will get cylinder-shaped, thick logs called "Timber".
That is NOT the wood you are looking for. To obtain actual wood that you can use to build walls, tools and all the other nice things, you need to put the Timber in your toolbar, and place it on the ground while selected, as if it was a construction block, then cut it down again with an Axe. This will produce "Wood", which can be used for crafting.

2. Cooking
To cook meat obtained from killing animals, you have to put it in your toolbar, select it, and then click on a lit bonfire or stone bonfire. Alternatively you can use a Furnace as well to cook, which is easier, in this case you simply put the meat in the central furnace slot, while on the bottom a fuel, which can be Wood, Timber, Sticks or Coal. And don't worry, meat cannot burn, it will stay cooked forever.

3. Satiety
Satiety measures how much well fed you are beyond the hunger limit. It works like this: when you eat something that gives you more nutrition than your hunger bar can contain (example: you have 9/10 hunger so almost full, eat a cooked mutton slice, which gives more than the remaining 1/10 in the bar) the "excess" food energy goes beyond the bar capacity and gives Satiety. You however cannot eat when the bar is completely full, so Satiety is efficient when you eat something that gives a lot of energy while the hunger bar is almost full, so most of it goes into Satiety.

4. Creating Coal from Timber
You can make Coal from Timber. To do this you have to build a furnace, fuel it with any combustible, and then in the central slot put one (or more) logs of Timber. Burning timber in the furnace will transform it into coal, so you can make Torches and start exploring the levels below the surface.

5. Removing furniture and walls
You need to equip the Glove tool, then click on the furniture or wall you wish to remove. It will pop out as a completed item so you can position it again somewhere else.

6. Growing crops and Infinite Water Source
To grow crops you need first to modify the terrain with a Hoe tool. Keep bashing until the terrain changes texture. Then use the Wheat Seeds as item onto the modified terrain to plant them. Now the crops will need water and light: light can be the one of Torches, so you can actually plant underground. For water, you need to have a nearby water source and dig a canal all the way to the field, or use Buckets, crafted with Iron, to transport water and then pur it down into a canal you built with a shovel. You can also build an infinite water source by digging a "+" shaped symbol into the ground, then putting 1 block of water to each external block: the water will converge to the central block of the "+" and if you only take water from there, it will generate a new water block infinitely.