Are the lower gears big or small?

A gear is always made up of (at least) two sprockets (or cogwheels), and the only size that matters is size in comparison, and which is input and which is output. This is also known as a ratio

For a bike input would be by the crank and outputwould be by the rear wheel.

You get a lower gear by making the input smaller and/or the output bigger, and you get a higher gear by making the input bigger and/or the output smaller.