  This is a pedagogical introduction to D-branes, addressed to graduate
students in field theory and particle physics and to other beginners in string
theory. I am not going to review the most recent results since there are
already many good papers on web devoted to that. Instead, I will present some
old techniques in some detail in order to show how some basic properties of
strinfs and branes as the massless spectrum of string, the effective action of
D-branes and their tension can be computed using QFT techniques. Also, I will
present shortly the boundary state description of D-branes. The details are
exposed for bosonic branes since I do not assume any previous knowledge of
supersymmetry which is not a requirement for this school. However, for
completeness and to provide basic notions for other lectures, I will discuss
some properties of supersymemtric branes. The present lectures were delivered
at Jorge Andr\'{e} Swieca School on Particle and Fields, 2001, Campos do
Jord\~{a}o, Brazil.
