The recipe and mining requirements
Place 3 diamonds in the top row of the crafting table and 2 sticks in the center of the middle and bottom rows. To get the diamonds themselves, you need an iron pickaxe, or better: a diamond pickaxe is not required to mine your own workpiece. Reference: Minecraft: pickaxe.
If there are five diamonds, leave two on the enchanting table. Additional Diamond Tools can be crafted later when Fortune appears.
Collect obsidian without losing a block
Pour water over a lava source: the solidified source will become obsidian. Water over flowing lava does not guarantee obsidian. Stand in a safe place, leaving water next to the mined block; it helps close the lava that opens from below.
First get one block and make sure it is in your inventory. For a minimal portal without corners you need 10 obsidian, for a table you need another 4. Do not transfer the rule with water to Nether: ordinary poured water evaporates there.
Covering the first frame and returning is described here: Your first Nether trip: secure a portal and find your way home.
Do not lose the tool while repairing it
Efficiency speeds up work, Unbreaking reduces consumption, Mending repairs with experience. Fortune and Silk Touch require different pickaxes. For the first 14 obsidians, a regular tool is enough.
A regular diamond pickaxe has 1561 durability, but does not disappear on a schedule: it is consumed by actions. Check the strip before a long descent. Mending does not return a pickaxe that has already been destroyed by a breakdown.
For table, shelves and enchantment compatibility, go to the guide: Planning enchantments and avoiding expensive anvil work.
