I am baking a two-tier cake for my granddaughter's first birthday. How do I apply edible glitter to the sides of the cake. I am using buttercream frosting.

First, make sure that it's actually edible, not a non-toxic product. If it says "non-toxic" on it that could be plastic glitter. I'd use sanding sugar or sparkling sugar instead of a glitter product, especially if a baby is going to be eating it.

To attach it to the cake, brush the cake with piping gel or corn syrup and press it onto the cake all over.

Just make sure the cake is cold so that he buttercream is firm before you start. If the icing is soft enough, on the other hand, you might be able to get it to stick without any piping gel. But I'd use the piping gel to be on the safe side.