Next year I'll start my bachelor's degree on mathematics, but I want to study something about it while I'm idle.
I've found this:
http://webdocs.registrar.fas.harvard.edu/courses/Mathematics.html
And this:
http://www.ufpe.br/proacad/images/cursos_ufpe/matematica_bacharelado_perfil_4904.pdf
They're syllabi from some mathematics courses, one of them is from the university near me, the other is from Harvard.
Can someone suggest a study way? Where should I start and which books I should get?
I would highly recommend you get an introduction to proofs from a good book. Other computational skills and methods can be learned easily during class, but proofs require some insight and a familiarity with a new style of mathematics when transitioning from high school. Toward this end, I would recommend, as I have to many others,
"Mathematical Proofs: A Transition to Advanced Mathematics" by Gary Chartrand, Albert D. Polimeni, and Ping Zhang.
There is an entire chapter devoted to each of the following:
With Three Additional Chapters online covering:
Try to get through as much of this as you can before you start university and you will be very glad that you did!