how to send fileor attachment from user1 to user 2 i.e both are account holder in same website

hi

guys

I hve to build an website in which user1 will send some ppt,file or any attachment to another user 2.

user 2 can see that attachment and can download it.

in this way i have to design the application

both user belongs to same application.

so how to fullfill.plz guide.