I want to study anabelian geometry, but unfortunately I'm having difficulties in finding some materials about it. If you could offer me some books/papers/articles I would be glad.
There is this very beautiful survey
Nakamura, Hiroaki; Tamagawa, Akio; Mochizuki, Shinichi
The Grothendieck conjecture on the fundamental groups of algebraic curves
You could also have a look at
Heidelberg Lectures on Fundamental Groups
Jakob Stix, Rational Points and Arithmetic of Fundamental Groups Evidence for the Section Conjecture Springer Lecture Notes in Mathematics 2054, xx+pp.247, Springer 2012. http://www.springer.com/mathematics/algebra/book/978-3-642-30673-0
This volume, Galois Groups and Fundamental Groups, edited by Leila Schneps has a great collection of articles, as does this volume, Geometric Galois Actions, including a nice article by Florian Pop on "Glimpses of Grothendieck's anabelian geometry."
If you'd like videos, here is a series of lectures on related topics, including a long series by Pop on anabelian geometry. At MSRI, you can find some lectures from Fall 1999, including one specifically about anabelian geometry.
Matsumoto, Makoto, Arithmetic fundamental groups and moduli of curves. School on Algebraic Geometry (Trieste, 1999), 355–383, ICTP Lect. Notes, 1, Abdus Salam Int. Cent. Theoret. Phys., Trieste, 2000.
has a nice concrete discussion of fundamental groups.
Florian Pop, Lectures on Anabelian phenomena in geometry and arithmetic (pdf)
Yuri Tschinkel, Introduction to anabelian geometry, talk at Symmetries and correspondences in number theory, geometry, algebra, physics: intra-disciplinary trends, Oxford 2014 (slides pdf)