The most usual action to be paid for is the "email submit"; i.e. they only have to enter their email address for the marketer to get paid. With some products, there will be an additional commission if the customer goes on to buy whatever product they've just enquired about.
CPA marketing using email-submit offers is very common on mobile devices, when you want to make it as easy as possible to get the customer signed up for a product offer.
The commissions for email-submit offers are usually only a few dollars, so it's a good idea to find offers that also pay you per sale as well. Or you could integrate these into your own sales funnel, and promote higher-priced items. The best option is to build a list which you can promote to every day.
There are many CPA networks to choose from, and you can see a wide range of both products and different networks if you go to http://www.offervault.com/ .
There's an interesting course about all this which you can find by clicking here.