I feel if you need to ask that question then you probably have nothing to contribute. Ask yourself this, what do you have knowledge about? How can you help people that come here asking questions? Do you have a sense of humour, if so do you know how to use it? You've been here since 2009, you really should know how to contribute by now.
I meant for example if I answer questions of people here, is it considered as usefull stuff? If yez, how questions I answer then I will promoted as premium?
If you're genuinely helping people out then yes it would be considered useful. You don't get promoted to premium, premium membership is something entirely different, you have to pay for that. You can get established if people "like" your posts, you have 2 at the moment so you only need 1 more to be established.
If I was a newbie and was in a bit of a hurry to get those 3 likes I'd spend some time on General Chat forum. Make a few comments, this will also help you to get a sense of the community here on DP. What you might want to do is to create your own thread on a subject that particularly interests you, and that you can feel comfortable commenting on. The general idea of this like system is to weed out scammers/spammers and to get the members involved. Good luck to you with all.