I posted how much and when in the recipe - just follow that exactly.
Here - I'll post it again.
Follow these directions:
Quick Red Velvet Cake
1 box yellow cake mix
1/2 cup oil
1 cup low-fat buttermilk
2 tablespoons cocoa
2 ounces red food coloring, see note
Combine cake mix with oil, buttermilk, cocoa, eggs and food coloring and mix well (we beat for 2 minutes). Bake according to package directions. Frost cake with Cream Cheese Frosting.
"Count yourself...you ain't so many" - quote from Buck's Daddy