How induce string method in main class?

You cannot execute qwe function in the main function, (I assume that is your problem), the reason for that is that your main function is static, whereas your qwe function is instance function. To do so, either change the signature of your function to,

public static String qwe(){

Or create a new instance of your czas class and then call that function, like,

public class czas { 
    public static void main(String[] av) {
        System.out.println(new czas().qwe()); 
    }

    public String qwe(){
        SimpleDateFormat a = new SimpleDateFormat("EEE MMM d kk:mm:ss");    
        String time=a.format(new Date());
        return time;
    }
}

This would work and will give you the result. You need to understand the difference in static and instance function — which many beginners do not know, so I won't blame you here.