Best "education" on how to get into modeling & the modeling world: www.newmodels.com or www.exploremodeling.com. Both sites explain how the modeling world REALLY works and how to get into modeling. Educate yourself so you don't get scammed. Also, check out www.modelingscams.org.
FYI - you don't need a portfolio in order to send photos to an agency. Any agency who wants you will know exactly what kinds of photos they want in order to promote you. Do NOT listen to anyone who says you need a portfolio in order to get started! I had nothing when my agency accepted me. When they signed me, they told me what types of photos they needed ("Commercial/lifestyle"), gave me a list of photographers in the area who did that type of photography, and I had to get photos taken for my comp card (model's business card which has photos on it). I didn't have to use any of the photographers on the list, I was free to go to any photographer I wanted as long as they knew how to do commercial photography. If an "agency" sends you to use their in-house photographer & don't give you the option to shop around for a different photographer, then it is a scam.
And keep in mind that since you are under 18, you will need parental consent before any agency will sign you. So get your parents involved in your decision and have them look at those sites above too so they know what you are doing is legit.
And lastly, modeling is a lot of hard work & you can't always do what you want. As a model, I have to make sure I get a lot of sleep, eat the right nutritious foods, and take good care of myself. Sometimes I can't go out with my friends because I have rehearsals for a show or fittings. You sometimes have to wait around for hours for a rehearsal or maybe at a photoshoot and you have to be very patient. Some models take their homework with them to shoots or rehearsals because they have no other time to do it. Modeling isn't all about lying around looking beautiful. The glamorous photos don't show how much work this really is. I don't say this to turn you off, I say it because people are often surprised about how much work a photoshoot is. Holding poses is tough and it sometimes reminds me of yoga because some of the poses aren't very comfortable at all but you have to try to stay relaxed and *look" comfortable. It's hard. Having said that, if you truly love to model, you won't mind the work involved.
To find agencies, do a google search on "modeling agency" + the state where you live. Avoid places like John Casablancas or Barbizon; those are "modeling schools" not agencies. An agency will not charge you for representation. Most legit agencies have sites online that tell you how to submit photos or when their open call days are where you can walk in with your photos & meet the agents.
Best of luck!!! :)
Me - I'm a model, signed with an agency in Detroit area.