how do i use the cotton gin
Sorry its unintuitive, I'm working on making it easier to understand how to create resources among other things.
You have to click on your colony name in the top-right, and then click on the Resources button. On the top-left scroll down to Cloth and click on it, and then increase the value and it will automatically create jobs to keep the amount of cloth at that level by bringing cotton to the cotton gin and creating cloth.