Do you have a good relationship with your parents? I gather by your profile that you are around 17? If so, and I know I am thinking like a mother because I am one, go to your parents immediately and tell them how you feel. They are your first line of defense and if they are supportive parents, they will get you the help you need. As far as how you should go about telling them, just be honest. If it is too difficult to verbalize, write a note.
If you do not have supportive parents, seek help from another responsible adult, perhaps a grandparent or a teacher, or a hotline if you prefer to remain anonymous.
Not to over simplify, but have you ever felt this way before? If you have, remind yourself that you got past these dismal feelings once before and you can and will do it again.
If you have not, remind yourself that there are so many others that have experienced the same dreadful mental state and have overcome their desperation with help, so you can too.
You are not alone in this battle we call life. I could get specific about my own journey, but I’d rather just implore you to seek immediate help from a trusted person.
Help is out there, but you need to ask for it!
Here is a link to a bit of psychology that may or may not help you with your thoughts: