It is very simple, (from my experience) it goes like this:
you must put their button (best would be header ofcourse for most of them :facepalm

, you know- header made from backlinks buttons

), then you have to submit your blog to whitelist, ofcourse don't except too fast reply, if you have luck they will whitelist you (2-3 out of 10), then feel free to submit your downloads there, i submitted my downloads 3 days ago and cant see them at almost 90% ddls where i submitted them. Effect: i have ~15 baclinks buttons, almost no downloads visible and i have to wait who knows how much long. That's effective marketing, isn't it? Ah, don't even try to remove their backlink, if they'll see it you're done, gg.
In shortcut that's how ddls works, maybe i have bad luck, who knows, time will show. gl hf
you can always pay, which in unbelievable way will increase whole proccess (i believe)
ps. didnt want to offence fair ddls B-)