well, the "-t" just means the type of filesystem and the "-r" just means "read only" (in other words, it's a shortcut for "-o ro"...
for example, if i wanted to mount "read-only" the first partition of my secondary master ide disk, which was formatted with the reiser filesystem:
mount -t reiserfs -r /dev/hdc1 /mnt/stuff
and if i wanted to mount it at startup automagically, then i'd need to edit my /etc/fstab...
/dev/hdc1 /mnt/stuff reiserfs defaults 1 2