UNIX permissions :
first digit is for the User himself, second one is tfor the user's Group members and the thrid is for all the Others.
1 is Read
2 is write
4 is execute
to know the access type of a file break down it's CHMOD so you know if you, your group members or everybody else can read/write/execute your file.
Some PHP apps like PHPBB2 require at least 644 to finish the configuration automatically.
To change it on a remote host use SmartFTP (http://www.smartftp.com) right click the file in the FTP browser and chage the access params in the properties box