I am trying to understand the best I can the d-brane theory. I have tried many sources and there is a thing which I don´t see totally clear, how the d-brane concept fit into type II superstring (no matter A or B). I mean, I can understand the argument that type II theories have in their massless spectrum antisymmetric fields and that that fields must arise from charged objects, and because hodge duality and all that the sources must be an extended object of the appropriate dimension. Also I believe that i rightly understand that you can represent the stringy one-loop amplitudes of type II theories by an efective supergravity action of point-like particles. That supersimmetry auctions (mainly their bosonic part) accept solitonic solutions that someway (which I don´t have totally clear) can be identified with the d-branes as described them before. Anyway, for me the big problem is how to fit the d-brane idea as expressed in any of the two forms i writed with the bosonic idea of the d-brane, that is, they are supposed to be hypersurfaces where the extremes of open strings must lie. But, of course, type II theories are closed strings, so that idea doesn´t seem to apply. Well, the solution most text say is "type II strings must have an open sector" but curiously I don´t see how these inclusion is actually realised. I guess that it can be related to a duality between type II theories and type I theory (which actually has open and closed strings, but I am aware that they are unoriented strings and that could be a problem) but I am not sure if i am right. Of course I know that all these is explained somewhere in many books of articles, but it is diversified over so many different chapters that it is a bit hard to follow he whole argumentation so if someone could explain all these I guess that not only me but a lot of people would be very acknowledged.