Your tool: Wooden pickaxe
Stash:
Click an item, then another slot to move or swap it. Shift + click sends it between the backpack and the hotbar.
Tap an item, then tap another slot to move or swap it.
The game
Dig from the grass all the way down to bedrock. Caves are dark: chop trees for wood, find coal and craft torches. Better pickaxes dig faster and reach rarer ores. Watch out for lava.
Deep under the start there is an abandoned mineshaft. Ride its minecart to a portal, and step into the Nether: magma cubes, ghasts, piglins and ancient debris for the best pickaxe.