In order to promote a mobile app using AdEspresso, you need to configure the app in Facebook, so that you can access it using your Facebook account.
You'll need to Register the app. You can do so here. This step is important, if your app is not registered on Facebook, you will not see the option to promote an app in AdEspresso when you click on "create new campaign".
An important step in configuring your app is to add your App Details to Facebook. If you do not complete this step as well as registering the app, you will see the option to promote an App but the App drop down will remain empty until you add your app details to Facebook. This is necessary to know where to redirect the user to download your application.
After you configure the App in Facebook, when you log in to AdEspresso and click on "create campaign", creating a Mobile App ad will become an option for you, properly displaying the app you have both registered and configured. The hard part is over!
If you just added your App on Facebook, you may need to Sync your Objects on AdEspresso: just go on the Ad Account page and click on the Sync button.
Once you select to promote an App, you can see you have some choices: Mobile App Install, Mobile App Engagement, and Desktop App Install. Once you click proceed, you can select the app you are creating an ad for.
The rest of the campaign creation process will be smooth sailing from here, just set your creatives, audience and budget and you are good to go!