Default [Q] How do Mobile Ad Networks put ads in our apps?

I make apps with tasker and I want to put them up on Play store in order to earn bucks, but they are not good/useful enough to sell directly. So I need to put ads and as far as I have read, I have to contact an ad network or two. But the problem is that I don't have programming knowledge at all! All I know is to make series of tasks and scenes in tasker and export them with tasker app factory so I have an apk file in the end.

I can make almost all apps which are usually seen in the top free apps' trends in Play Store.

So, how will I put their ads? Do they give something which involves the use of Android SDK? Or can I give them my apk file so they will incorporate their ads for me? (this doesn't seem safe though).
One solution for this may be that they give me HTML for the ad so I can put it in tasker's HTML box, but then the ad networks won't be sure if their ads are showed properly or I am showing something else over the HTML box.

Also, do I have to pay the ad networks in advance or do they only take the share from the advertisements' earnings?
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