Buckets are quite expensive in Minecraft, especially in the beginning, and not everyone has a sea or lake lying next to their base. Fortunately, you can create an infinite water supply so you don't have to walk halfway across the world for a bucket of water.
Step 1. Make sure you have two buckets
If you don't have buckets, mine some iron and melt it in your furnace to make iron ingots and then make the buckets. You can do this with one bucket, but it will take longer.
Step 2. Go to a sea or lake and fill the two buckets
Step 3. Make a 2x2 square in the ground
It should look something like the image above.
Step 4. Fill a corner of the room with the water from the bucket you just got
It should now look like the image above.
- Fill the angled corner with the other bucket of water you got.
Step 5. Voila
You have an infinite water source!