Recently, I accidentally screwed up /etc/passwd/ and I thought that I could use an sd card reader. Turns out, I can only access boot and RECOVERY. The computer we are using is a Mac. Is this the only folders the sd card allows us to access, and how do you get into etc?
The boot directory is formatted with the FAT file system. I guess RECOVERY is as well. That means the contents are readable and writable by Windows, Macs, Linux as they all support FAT.
The other directories will be formatted as ext4 which is a Linux file system. You will probably need to find (i.e. web search) an add-on to allow this file system to be read by non-Linux systems.
The simple answer is you Can't - it used to be possible with 3rd party add-on, but since Apple introduced SIP all the external programs fail.
Your best bet is to use a live Linux CD or similar.
You can boot the Pi into the root shell and fix/change password
I should add that there is NO REASON to edit