Hi Bekka,
First of all to officially be considered "Jewish" you must have a Jewish mother, or go through a conversion process. Orthodox and Reform Judaism offer two different options for converting (Orthodox is more strict and widely accepted...Reform conversions are not accepted by Orthodox Jews). Since you are 14, I would recommend continuing to learn and try things and consider conversion once you are 18 if it feels right for you.
To celebrate Passover, the best thing to do is try to find a seder (Passover meal held on the first two nights - this year, Weds Apr 8 and Thurs Apr 9) in your community. Try calling a local synagogue, or searching on chabad.org to see if there is a Chabad house in your community. (Just be aware that Chabad is a particular sect of Orthodox Judaism with certain beliefs not shared by all Jews - however, they are also extremely welcoming to all people interested in learning about or observing Judaism, which is why I am recommending them for a seder!)
Regarding food, Jews do not eat any products with wheat, barley, oats, rye or spelt from sundown on Weds Apr 8 until 1 hour after sundown on Thurs Apr 16. (These dates change every year because Jewish holidays occur according to the Jewish calendar, which goes by the moon and is different from the secular calendar which goes by the sun). These products are considered chametz and are forbidden during Passover, as well as any products containing them. The only time grains are allowed are when they are baked in matzah, in a special process supervised by a rabbi to ensure that they do not rise (leaven). Foods that are kosher (allowed) for Passover will be marked on the box - there are many different accepted symbols such as a U inside a circle - symbols vary depending on what rabbi or authorized institution gives the certification. It MUST say kosher for Passover, as many items that are kosher the rest of the year are not ok on Passover. Additionally, Jews whose families come from Eastern Europe do not eat rice, corn, beans, and other legumes (these are called kitniyot, literally meaning "small things")...this includes items with corn syrup.
Items that do not need to be specially marked include fresh fruits and vegetables. Eggs, fish, and dairy are also fine if you eat those.
Try asking in your local supermarket if there is a Passover section.
Please also be aware that the majority of Jews in America are not that strict about following the kosher restrictions for Passover. I.e. most do not worry about corn syrup, or just avoid bread, pasta, cake, etc - obvious type items.
I would recommend looking for a few Passover items in the grocery store like matzah (honestly matzah is kind of gross!!), trying to participate in a seder, and continuing to learn about the holiday. THere are a lot of good resources online, I will link a few reputable sources below for you. (These websites are also good for learning anything else about Judaism as well!!)
Good luck with your learning!