What a big question! First off, you are not alone in questioning your sexual orientation. Know that many, many, many people are also and have also asked themselves those very same questions.
Second, know that no one but yourself can find the answer! It's YOUR identity, and no parent, friend, mentor, or stranger can figure it out for you. This can be both terrifying and liberating.
Third, there isn't a "wrong" answer. Even if you later identify differently, whatever you identify with right now is still valid. It just becomes valid in the past tense. So, don't worry too much about being "right" and finding the "right" answer. Sexuality is often very fluid.
Fourth, it may help to read. Find out what each definition means. Listen to the stories of people who identify these ways. What does it mean to them to be gay, lesbian or bisexual?
Fifth, give yourself time. It's okay if it takes weeks, months, years to figure out. Just go with it. It took me until my second year of college to figure out my sexuality. You don't need to tell anyone until you are ready, and you don't need to label yourself unless it's what YOU want and it helps YOU.
Finally, it may help to journal to sort out your feelings. You might also seek out the LGBTQ community in some manner - online or in real life - to find support and information as you explore your feelings.
Best wishes friend. It'll all turn out okay in the end. :) Just breathe and give yourself the time and space to explore your feelings and thoughts.