You have to email michaelson@tapasmedia.co to turn on tipping.
Here's the official anouncement on tipping with basically all you need to know about it:
I'm not that well versed in how ad revenue works, but views and ad impressions are different, Tapas takes 25% (I think) of your ad revenue to run their site, and since it's wired through PayPal, there are a couple of other fees I think. Other than that, Ads only make fractions of a cent per view, so ads just don't make much money until you have a lot of ad impressions.
Disclaimer: I'm not in the ad revenue program myself so I don't know how it works, but this is what I've heard.
Keys work like this: in order to view episodes, your readers will have to purchase keys with Tapas coins that can be bought with real money or earned by watching ads (but you only get like 10-30 coins per ad).
Disclaimer: I'm not in the key system so the rest is what I've heard.
Each key your readers buy is worth a certain amount of Tapas coins and those coins are turned into real money for creators. I think keys are an exclusive thing, so if you want to enable them you'd probably have to talk to Tapas' editor in chief: michaelson@tapasmedia.co, but I think you have to have a really big comic in order to get it enabled.