Not knowing what will happen is part of what makes contact hard, so here is the shape of it. This section is practice, not law.
The shape of it. Someone answers, or replies in writing. It is usually a trained volunteer, a counsellor or a peer rather than a doctor. They ask what is going on, and you do not have to have an answer ready; silence and false starts are normal. You can stop at any point, hang up, close the chat or simply stop replying, and you owe nobody an explanation for it. Many services do not ask for your name, and you are allowed to ask at the start whether you have to give one. Nothing is decided for you in the first minute. If you cannot speak out loud, because you share a room, the walls are thin, or speaking is hard for you, text and online chat exist for exactly that. Find A Helpline shows which services take text or chat.
What can go wrong. You may wait. Lines are busy and some open only certain hours. A first conversation can feel flat, or the person may simply not be a fit for you, and that is not a verdict on you or on the next one. Some services are built for adults and sound like it.
What you can ask. Before you say anything you can ask: is this free, is it recorded, do I have to give a name, who else sees this, what happens if I stop replying. Those are ordinary questions. If a service will not answer them, that tells you something too.