If you would like to copy a file from your home directory you could use either of the following:
$ scp remoteusername@host:fileiwanttocopy /my/local/comp
$ scp remoteusername@host:~/fileiwanttocopy /my/local/comp
~ will evaluate to the logged in user's home directory.
If you woul like to copy a file from another user's home directory you would use::
$ scp remoteusername@host:~anotheruser/fileiwanttocopy /my/local/comp
~anotheruser would resolve to the user "anotheruser"'s home directory.