Your host says 755 to give what permissions?
On most typical server configs, 755 will do a rwxr-xr-x, whereas a 777 will set the permissions to rwxrwxrwx. r stands for read, w stands for write, and x stands for execute. The first block of three letters is owner, the second is group, and the third is other.
A dash (-) in between letters means that the attribute for that function is disabled. In the 755 example, the owner can rwx, the group can rx, and others can rx.