Where could I find a simple sample for download a file after login?

Android Core V2. I need a simple task that logs internally and then download a file. Only one action in a button. It is not complicated... but really for me it is.

My Java and android is poor, but I thinked that there is no problem with the example proposed. I checked the example with a lot of files that I don't need and I started adding files and analyzing the code to know how it works. Well, for me doesn't work. There are a lot of exceptions because you need libraries and have to add them to the project but after 4 days trying to solve different problems I give up.

I hate using support.v7 library because always cause me problems. I don't know why I have to use Picasso because I don't want to download photos. And after download a few libraries I have to stop when a java.lang.noclassdeffounderror apears due to com.squareup.http.okhttp.client. I read that Picasso use an old version of okhttp and also that I don't need okhttp library but there are neccesary for the example so at this moment, after 4 days, I never did a login succesfull.

It is my point of view that, first of all, we need simple examples and, after that, complex examples for experts. I cannot walk if I can do the first step.

I ask about a simple example for download a file with a simple button, no need list, folders, a complex view, etc. It is possible?

Thanks