If you are buying extract kits, the grains that come with the kit will all be ones that are steeped. Grains that have to be mashed will be Base Grains or Base Malts. If you look at some raw materials on websites, you should see grains separated into these categories. It has to do with diastatic power of the grain, its ability to convert starch into sugar. Your steeping grains will have little to no diastatic power or will need the help of other grains for conversion. After you have done a few brews, read up on all grain brewing, then partial mashes and it will make more sense. You might want to switch over to partial or all grain later.