A seed is a code for a randomly generated world, when you make a new world you have the option to type in a seed code. Since seeds are so random codes can literally be anything from 123 to abc and words and phrases. Each one getting a random result. Say for instance.
You enter 123 as your seed for the world, and the world spawns you in a hilly area with trees on the outskirts. If you like this kind of territory you can re-enter the seed, 123 into any new world you make to get the same zone again. Minus any progress you made in the first one.
Seeds are endless and every world has one regardless of wether you assigned one or not.
OOOHHHH. Ok, Now I understand what that means when I start a new game. Thanks kind sir.
Well, im on a world, where there is A LOT of water, and beaches. I had to walk quite a distance to find some grass and trees. Need that wood yo.
And I found a cave, went in it, heard some groans, immediately turned around and was like.........
I didn't want to go in there anyway.