You can interact with the contract with myetherwallet, Parity or Mist/Ethereum Wallet. All three systems work similarly.
There are two kind of functions in the smart contract:
a) Functions where you just read out info from the contract. You don't need your wallet to read out infos and it doesn't cost gas. The only important read out is the check of the voting, i.e. you can read out how many people voted for or against a proposal. This function is called "voting"
b) Functions where you change something on the smart contract. You need to execute these functions with the wallet and they cost a small amount of gas/Ether. At the moment the important function is called "vote" where you vote for or against a proposal
Every proposal is identified by a number. Number 1 was a test proposal, our first proposal will be number 2. So if you want to read out the results of a voting or vote for/against a proposal, you need to enter this number
Futhermore you need to know the address of the contract: