I see in explorer that forging reward is zero.
when reward will be enabled ?
Block number 75,600 (~ 6 days from now)
is that like mining or staking or how? How will you be able to get rewards? buy certain amount of coins then keep in wallet or run a node or how?
I think most of your questions since this one can be explained by this article
https://blog.ark.io/dpos-and-ark-voting-explained-68596a171ca1#.4w89a9wr8TL;DR ARK uses a DPoS consensus mechanism, which means a set amount of delegates (51 in arks case) authenticate all blocks on the blockhain. So if you simply hold coins either on the exchange or in your wallet you won't get any block rewards or fees. If you want some of those you are going to need to registered a delegate and gather enough votes for it to be in one of the top 51 positions. 1 ark = 1 vote.
How much vote you are going to need to be in top 51 is an open question depending on how much of the total ark is participates in the voting process. For Lisk it's less then 30%, if it will be around the same for ARK a delegate would need about a minimum of 500-600k ARK vote weight behind them to make it. But it's not a set amount, this is like trading the market (the coin holders) decide. Right now now you could be voted in a much lower amount, but if other delegates increase their weight then it's a numbers game.