How can I make people understand me better ?

The problem is that when I talk about something people understand «what I am not actually asking for» and they think that I don’t understand them or I don’t understand at all so the communication is blocked because either I don’t make myself clear about what I want or just the ideas that I communicate do not get trough the mind of my recipient and as a result they think that I am stupid to ask the thing twice but actually it’s not what I am asking for.
Am I making my self clear guys or do you think that I am crazy ?