SETUP THE DEFAULT FILE PERMISSION

Sometimes, if we don't change the default permission in linux after we make a new file, that's can't be edited cause the file default perimission for the file is read only.I think it's not so comfort if each we make new file we should change the permission first if we want to edit that. We can use umask command to setup the default permission for the file that have been created/make. The Syntax is like this :
lambanx@fresh-IDEA # umask [permission]

Example :
I want to setting the default permission for the file that have been made to full access for user,group, and other
lambanx@fresh-IDEA # umask 777

the 7 number is represent full access permission for the file, why the there are three 7 number above? cause i would like to setting permission for user,group, and other.