As you can see here, you can set each column's width to a certain number of pixels, or as a percentage of the entire width. You shouldn't have to mess with these to use this form, unless your site needs a more narrow display.
Notice the other options on the left as well. We can set certain criteria for the records we want to show in our display, filtering by date or other factors. However, I want them all going backward in time, so didn't make any changes to the defaults. Feel free to check out each option, but don't change anything unless you need to for your site display.
Next step is to click on the "Access This Application" large button and go to the next screen.