This is tough, but not impossible. I know you're scared. Although I'm straight, I have more than a few gay and bi friends who went through this.
Let's deal with your parents first. It seems like you are at least fairly intent on "coming out". Be direct. Decide on your moment, which is best when they can focus on what you are telling them with a minimum of distraction. Don't call them at work. And don't do it when they're under enormous amounts of stress either. Remember that they may go through a whole series of emotions ranging from sadness to anger to frustration to self-criticism. None of this is your fault. They are just processing a very big piece of information, and they may need a little time to adjust. If they are loving parents that are in tune with the modern world, things should slowly but steadily settle into place. And all will be well. In the end, they will be thankful that you were honest and proud that you were brave enough to speak up.
As for your friends, just TELL THEM. If they're your true friends, they will accept you. Again, they may go through a few emotions. Especially if you've been friends for a very long time. Give them a day or two to sort it out if necessary. (Although to be quite honest, a very good friend will be there for you RIGHT AWAY.) But remember that they too are processing a big piece of information. Ideally, they'll accept it right away and be your source of support throughout this time.
Be careful with anyone who may try to "convert" you to straight. Although some of your loved ones may experience a bit of denial, which is normal, they must fairly quickly accept this as the truth. (I say this with the assumption that you are already absolutely sure that you're bi.) Don't let people scare you or bully you into being something that you're not. You will only be lying to yourself and creating a whole other set of issues to deal with.
Lastly, get in touch with a gay/bi support group. You can find these online or in a phone directory.
Be brave. Be honest. And best of luck.