How do I tell my parents?

Well I will tell you the TRUTH. If you go tell your parents that you are suicidal > what they will probably do is call the Police and have you taken away for your own safety. This is what usually happens, in fact it has happened to me at least 5 times. SO I know the drill down completely.
They will call the police and say my child is talking about suicide. The cops will then come and take you away and bring you to a Psychiatric ward where they will keep you for at least 3 days or more. Usually its between 3 days and sometimes up to 10 days or more in some circumstances.
They do not arrest you.. but they will have to take you away to a psych ward for your own safety.
When you are in there… it is a locked down situation which means You cannot leave until they release you. This is a routine safety measure that has been enacted in the USA and other parts of the world. If person says they are thinking of suicide that is what happens. They have the right to detain you in a pyshc ward for 3 days or more for a psychiatric evaluation. While you are in there you will have to see a psych doctor and they will put you on medications for depression. Also while you are in there they will make you go to group therapy a couple times a day where you have to discuss issues like depression and coping skills and anger management and things pertaining to mental health. Also at different times you might get to see a therapist one on one who will ask you questions like > Do you have thoughts of suicide??…. and so long as you say YES I am thinking about suicide. They will keep you in there longer and try different medications on you and continue to make you go to group therapy. If you say NO I am no longer having thoughts of suicide then they will keep you for a couple more days… and if they think that you are no longer suicidal > then they will release you and you can go home… with medications that you have to take at home.. and then they will set you up with an outpatient center someplace where you will have to see a psych doctor like once every 3 months and they will keep prescribing meds for you to take at home on a daily basis. The outpatient doctor will continue to ask you if you are suicidal? and if you say yes they will stick you back in the Psych ward for your own safety.
Usually if a person has been in a psych ward they will try to keep you on medications for at least 6 months or until they feel you are doing better. If a person actually has a suicide attempt but does not die… its pretty much the same routine.. only they THEN will try to keep you on medications for at least a YEAR after the attempt. I have been through both of these scenarios several times and I can tell you being in those places is really not that fun.. but its also not that bad. In fact I actually enjoyed my stay in some of those places and got a lot of help I needed in life.
Usually the psych wards are COLD> sometimes they are dirty. You are usually in there with people with all kinds of various mental health problems. Sometimes there are homeless people in there. Sometimes there are people who can get aggressive with other people in there. Sometimes there are people who have overdosed on drugs and are recovering from that. You have no privacy when you are in there. You usually cannot wear your normal clothes when you are in there and its really not that fun to be in those places. Again I have been to these places several times > so I know the routine. When you are in there the main goal is for them to get you on medications and to get you to do the group therapy thing. They will KEEP You in there if you keep saying that you are suicidal. See the mental health field these days views people who have suicidal thoughts as a sickness that needs to be corrected by medications and therapy. So they will try different types of medications on you until you say that you feel better and no longer have suicidal thoughts. If you have never been on Psych meds and wind up in those places and they put you on heavy meds > you might feel very drowsy and sleepy when you get on them. Some of the medications make you hungry and want to eat a lot of food. Other medications can also distort your vision a little bit and you wind up seeing everything in like blury way.
When you are in there the only thing to do > is take your meds. Sleep in your room or rest, go to group therapy when they have it (usually 2 times or 3 times a day) , pace the halls if you want, go to breakfast, lunch and diner when it is served and sometimes in the nicer places they might have recreation room that you can go to once a day and read magazines or play games or play ping pong and stuff like that. They sometime might have piano or some other musical instrument in the rec room in the nicer places. The only other thing to do > is sometimes they have a phone in the hall you can use at various times and you can call somebody from the phone and chat with somebody. This is basically what will happen to you if you tell your parents you are suicidal.
Now if you are really suicidal then this might be a good thing for you. Because being in a place like that really does help a lot of people. and when they get you on meds the meds can sometimes really help out and you might wind up coming out of there feeling much better with a whole new perspective on life
I am just telling you the truth because I have been through this a number of times.
I would rather see you go in there and get on meds and get some group therapy then for you to try and end your life. I do not know your age > but you sound like you are young.
I will tell you > you might think that suicide is the way out of your problems right now > but its not. I think you need to get some help. Meds and therapy can really help people and you can come out of there feeling much better about life and be able to carry on from there and go on living and be happy. Again I have been in those places several times and each time it did help me and i did save my life.. and now I am alive and I have a good life and I am glad to be alive.

Good luck