There are three ways to access a file in a file system:

Relative file name like foo.txt. This resolves to currentdirectory/foo.txt where currentdirectory is the directory currently occupied. So if the current directory is /home/foo, the name resolves to /home/foo/foo.txt.
Relative path name like subdirectory/foo.txt. This resolves to currentdirectory/subdirectory/foo.txt.
Absolute path name like /main/foo.txt. This resolves to /main/foo.txt.