Okay I don't bake too may big cakes so I haven't needed to use a heating core yet. How do you put them in the cake, does it stand up on it's own, what do you do with the hold in the middle of the cake in the end? Sorry for such a silly question

I don't think it's silly. If you're using a flower nail, spray it with a little no-stick cooking spray and place it in the bottom of your pan flat side down. The pour your batter over it. After you've removed your cake from the pan, while the cakes warm remove the nail. You can actually peel off any cake that stuck to it and fill in the hole. Or just fill it in with frosting.

If you're using an actual heating core like Wilton makes (for stand-up/3D cakes), you grease and flour the core, insert it into the pan and then pour in your batter. You can then grease and flour the inside of the core and fill that with some batter. That will make a plug for the hole if you decide not to leave the core in. If you do decide to leave the core in, don't grease and flour it. It will be more stable if the cake is stuck to it.

I used a Magic Line core in the 12" x !8" cake I baked this week (half choc/half white) and I don't believe it did anything to help the cake bake! I put batter inside it, and used that to fill the hole when I iced the cake...the whole process seemed like quite a bit of trouble for not a lot of improvement. Just cutting the temperature to 325 F seems to be more reasonable and effective. Janice