You will need to make an iron pickaxe or better (diamond also works). This is made by placing 3 iron ingots (smelt iron ore) in the top row with two sticks in the center of the other two columns.
With a shovel
Leather is harvested by killing cows.
no, you can destroy them, but it is only uncommon they will drop seeds
Use wheat which you can harvest/steal from villages
If you run water over a lava source block you will create obsidian. Mine it with a diamond pickaxe to harvest it.
The only way to acquire fire blocks in Minecraft 1.2.x is to use inventory editors.
You cannot harvest plants in creative mode because you have all the resources in your creative inventory! So when you harvest a plant, it just breaks.
Put a pumpkin in the crafting table or self crafting
In order to collect diamonds in Minecraft, you have to have an iron pickaxe, if you are wondering how to get iron, you have to have a cobblestone pickaxe and find the brownish looking ore then mine it. Once you have it, you need to cook it into iron ingots then craft an iron pickaxe then there you have it.
You need a Diamond Pick to harvest obsidian blocks.
You still have to harvest and feed them by hand.
Well, darling, in Minecraft, you'll need a good ol' fashioned tool called a "hoe" to harvest those crops. Just grab that hoe, give those crops a good whack, and watch them pop right out of the ground. So, go on and get your hands dirty with that hoe - in the game, of course.