Travel advice? Ahhh! Help!!!?

Ok, well I have NEVER been on an airplane. I’m 16, and this summer I’m going to Costa Rica with spanish teachers, and then after I get back from that 2 week trip, I’m flying to Florida BY myself to be a nanny for about a month…I’m so nervous!!
Any advice about air travel? And more advice about when I go by myself? I’m way scared…also, what to pack? Can you bring a pillow and blanket with you on the plane?