You have a /mnt directory already. Do this to see:
Then do this:
ls <that is a small L>
You should have these
When you type in mkdir /mnt/cdrom it should put the new directory inside the mnt directory above. Linux will not mount to a directory that does not exist. You can type in cd /mnt and then do ls <that is a small L again and short for 'list'> you should see the directories cdrom and floppy if you have one.
If you don't have a /mnt directory I don't think it will even boot at all. It's there.
When you log in as root it puts you in the /root directory listed above. If you log in as a regular user, not root, say like Txlyo the you would be in the directory /home/Txlyo then.
I suspect that you are new to Linux. If so let me know, I will give you some links. Linux is not set up like windoze as far as the directories are concerned. Windoze is register based and Linux is file based. It is about as different as night and day.
Post back with a few questions and let me know if you are new. You may also want to update your profile and put in what country you are from and the distro. You don't have to put the city, just put in what you are comfortable with. I put in my state and country. Nobody will find me.