i'm trying to understand what those dapp are, are they some sort of contract that you can purchase on the ethereum platform?
Are you talking about my post (the mining of ethereum)?
I think it's a general question on the nature of DAPPS (what they are, what they're for).
Here's a great tutorial site that explains things pretty well.
https://dappsforbeginners.wordpress.com/Of particular interest within the context of the original poster's message, are these few paragraphs:
The basics
Ethereum enables the decentralised web, referred to as ‘web 3’. What makes it different from web 2 is that on Ethereum, there are no web servers, and therefore no middlemen to take commissions, steal your data or offer it to the NSA, and of course nothing to DDoS.
A Dapp (‘decentralized app’) consists of two parts: a frontend, written in HTML, and a backend (think of it as the ‘database’ for your frontend).
Good news: if you like bootstrap, or any other framework, you can continue using them, as the frontend of dapps have full network access, and CDNs are accessible. In fact, for all intent and purposes, developing a frontend for a Dapp written HTML is the exact same as developing a website, and converting from web 2 to web 3 is in many cases trivial.
Even better news: you get reactive programming baked in (which should please angular, meteor and derby fans), by simply using callback functions, and there’s no new framework to learn.
Even even better news: because Ethereum relies on cryptographic principles to function, every Dapp knows the pseudonymous identity of each user. That’s right, users won’t need to ‘create accounts’ or ‘log on’ to access your dapps, and you can think of this as open ID by default, everywhere.
There is no bad news, except maybe for the bad actors from the web 2 world, such as dishonest exchanges running with the money or gambling sites falsifying random number information to make a quick buck. On Ethereum, the backend operations are validated by all nodes on the network, meaning that a backend will always will do what its code says it does. This is why you might have heard people call Ethereum ‘trustless’ – there’s no need for users to trust into a central authority to ‘do the right thing’.
Hope this helps.