While you can't create your own ads in impact.com, you can request new ads from the brands you've partnered with.
From the top navigation bar, select Ads → Ad Requests.
From the top right corner, select Request New Ad [Drop-down menu].
From the drop-down menu, select the type of ad you want to request.
Optionally, add some creative suggestions to give your ad a better chance of getting approved.
You can upload an ad creative by selecting Choose File next to Optional Example.
You can add some creative direction (ad size, preferred colors) by writing out your suggestions in the text box next to Additional Instructions.