I bought the Lego Kit LEGO Crazy Contraptions. It allows the learner to build a blender. My son, the engineer, said something to our grandson, his son, about a gear ratio. Can someone translate?
A blender spins very fast, presumably faster than the motor supplied in that kit. A gear is a pair of cogs which mesh together to change the rotation speed. If a cog with 20 teeth meshes with one with 10 teeth, then for every 1 turn of the large cog, the small cog will turn twice. This is known as a 1:2 gear ratio, or just a ratio of '1/2'.
So to make the blender spin faster, you need a smaller gear ratio. The ratio is input:output, so you can also take a pair of cogs with a larger gear ratio and turn it around.
There's a good article on wikipedia.