Personally I've found stryofoam hard to work with because of it's lightness it moves too easily (you must figure out a good way to ancor it down first). You can use anything that doesn't absorb your frosting.... a filled heavy plastic container, the side of your computor, BUT, put it on a turn table so you get familar with using the turn table at the same time! Because using a turn table is part of the skill.
Baking cakes is part of the skill too, you need to learn that as you go....SO why not make a real cake to learn on. If you make something dense like a carrot cake you can even scrap off all your decorative work and re-do it many times. Store it in the freezer for a couple days, whatever (so your not baking it fresh each time), actually piping boarders on it will be easier if it's frozen. There will be occassions where you need to know how to salvage a real cake and refrost it.
Also you must use frosting to learn frosting.
When your working on a "dummy" surface you just scrape it off and re use it over and over. Just like I'm saying you can reuse a cake over and over.
When your learning boarders just pipe them dirrectly on your table. Then scrap the frosting off with your palate knive. To learn them on the side of a cake frost your dummy with a base coat of frosting first (again to simulate what it's like on the real surface).
You could even frost your counters at home and pipe on the side of them too. The only thing you can't do is put them on a turn table. They clean easily.
