For my daughter's birthday this year we celebrated it on Easter so this birthday cake has a Easter theme, but here is a basic idea for any birthday cake.
I use box cake mixes, this was a spice cake mix. Make as directed and pour half of the mix in one 8" round pan and the other half into another 8" round pan. Spray the pan well before pouring the mix in, you want it to come out easily.
While the cakes cook(according to box instructions) you'll want to get your decorations ready for the cake. I decided to use Easter candy to decorate it and around our house Sixlets are a favorite. You can use any favorite candy for this really.
I took some cream cheese frosting (again store bought but you could use homemade) and I used food coloring and died it pink to use it for decorating the cake.
You then put the frosting into a zip lock baggie (my version of the expensive ones the professionals ones use) and I set aside until ready to decorate.
Once the cakes are finished cooking, you want to leave them in the pan for about 20 minutes. After that you can get them out of the pan. If they are still to hot, wait a bit longer before taking them out of the pans. This is my technique(if you really can call it that) of getting the cakes out of the pans. I use a plate first, than I put them on a cooling rack to completely cool before decorating.
Once cooled and ready to decorate, I cut off any rough edges on the cakes and round it up a bit.
This will be a layered cake. Frost the rest of the cake, all of it. Decorate with the candies and cut a small tip on the edge of the zip lock bag and pipe your frosting however you'd like. (sorry I needed both hands for this part and couldn't take pictures but it really is simple)