What is the main goal of Minecraft?

In casual playing, there is really no goal. However, if you're trying to beat the game, you'll find there is one. Your main goal is to defeat the Ender Dragon and see the credits roll.

What is the most efficient way to get this? Now I will tell you the common speedrun method of beating Minecraft (1.16+). Hope you enjoy!

Overworld

As soon as the world loads, trees are the way to go. A full tree is advised, and you should craft this wood into a crafting table, and some sticks.

Using the wood and sticks, craft up a wooden pickaxe and dig into the ground. Gather three cobblestone by mining three stone blocks and craft a 

                                    stone pickaxe.

From there, mine more stone and make a stone axe and shovel, and a furnace. If you see a village, go in and break the hay bales to make bread for food, and kill the iron golem. The way to do this is to stack up three blocks after hitting the iron golem. Jump on your pillar and hit him as you fall to get a critical hit. Do this until he dies. Free iron.

Whenever you find iron, village or no village, craft a                                                a flint and steel.

Look for caves. Gather iron for two buckets and whatever else you need (recommend- a shield, iron axe, and iron pickaxe + buckets). Then, look for a lava pool, or ravine with a decently sized lava stream.

Building the Nether Portal

It might be difficult, or it might not be. First, make sure your bucket has water in it. The other one should be empty. Find a 1x4 strip of lava in the lava pool, and place a block on either the second or third block. Next to it, on the either second or third block, place your water. Then, break your temporary block. The water should flow to the next space, creating the bottom of the portal.

The next part is harder to explain. Create an upside down "L" by placing 3 blocks up and one block in the front on the very top on the left side of the portal. Break any blocks in the second column, and leave only two blocks on the right side- one at the bottom of the third column, and one at the bottom of the fourth column. Then, place your water on the side of the upside down "L" (the right side, facing the rest of the blocks). Using another bucket, scoop lava from the pool around you and place it around the portal where the obsidian should be. Obsidian should form. Remove the water when the portal is complete.

The Nether

The Nether is a place where you can easily die, so be careful. The shield is very useful here.

If you spawn in a Crimson Forest, gather any gold ore you find. This can be used to trade with Piglins for Ender Pearls.

If you spawn in a Warped Forest, don't worry. Endermen spawn here very often, so you should be able to get Pearls more efficiently than trading.

If you spawn in other biomes, then you should make sure to gather gold to trade with Piglins when found.

No matter what biome you're in, the goal of the Nether is to find a fortress. Look around until you've found one (it could take hours, or you could have one at spawn. Like other buildings in the game, they are randomly generated.) When you find one, you can loot it while looking for a Blaze Spawner. Once found, kill the blazes as they spawn. This is where the shield is most useful, as they shoot fireballs at you. Each Blaze rod gives you 2 Blaze powder, so you should get at least 8-10 rods.