I made a two layer demo cake last weekend with no dowel rods because I didnt know you needed them. Is this a precaution or a MUST? My instructor/friend said that I have to use these in order to prevent collapsing......which makes sense but I am not sure how to do this. Also, the bride is wanting to freeze her top layer for anniversary, can I put a piece of cardboard between that layer so its easier to take off the top? suggestions help would be great! Thank you

A must. Anytime you stack another cake on top of another you need dowels or some kind of support. A cake should never (at any time) be resting on another cake. It will collapse.

Each cake must be placed and decorated on a cakeboard (available at Michaels). Then either use the column supports (Wilton), SPS (online Bakery Craft) or dowels (cut to the same height where one dowel is cut to the height of the cake tier it is going in). The cake board then is placed on top of the dowels where you can do the border/finishing decorating.

Here's a link that should help with construction. IMO dowels are a disaster waiting to happen. You'd be better of with the SPS system (sticky note in the "How Do I" forum) of Wilton hidden pillars. http://www.cakecentral.com/article23-Teired-Stacked-Cake-Construction.html

Edited to add link

Yes, you absolutely need the dowels for support, you can use the plastic ones, wooden dowels or sucker sticks work well also. ( the longer ones) I have heard of using straws too but that would scare me. You need the cardboard also to fit the size of the cake layer. What I do is lightly apply 10x sugar to the top of the cake that I am putting another one on, just enough to cover the cardboard circle that is going on the other layer so that it will prevent the board from sticking to the icing when you take off the cake. so if you have a 10 inch round and are putting on a 8 inch cake on top cardboard should be 8inches and I usually use a shaker to apply the 10x to the top of the 10inch being careful not to go to far otherwise you will see the 10x. It usually works quite well so you are not losing the icing. I hope that this helps.

You said that you make a 2 layer cake, did you mean 2 "tier" cake. There is a difference. If you made a second tier, ditto the other people, you must use some type of support system or it will collapse.