plz help !!!!

I want to establish an app for students and instructors to help them facilitate their work 

I want the students to register on that app and doing some task like downloading files,taking notes, photos,sound records

, and I want these information to be saved in each user account , so when the user sign out and login again all the information are there nothing lost 

?? is that possible with app inventor 

Sure. Do the tutorials first and you will find out.

As suggested by Ghica do the Tutorials:

MITs tutorials    http://appinventor.mit.edu/explore/ai2/tutorials.html

To learn how to program with AI2, read the AI2 free online eBook  http://appinventor.mit.edu/explore/ai2/tutorials.html   ... the links are at the bottom of the Web page.

You can save information on a single device using the TinyDB but then it is not easily shared with others.  If the saved information needs to accessed by others, you will need a TinyWebDB or a Fusion Table.    How to use these controls is described in the links above.

You want to do a lot of things and that is a lot to expect from a single Android app.  Can it be done?   Probably, but you first have to learn how to use the programming tool.    You do that by building small projects that do part of what you want the final, large project app to do.    Once you get the small projects to work doing specific tasks you can consider building the project you want.

When you finish a small project, and you need more information, ask again here in the forum and you will get specific advice.