I am always guessing what i have to mount. is their a command that will show me all then devices that i can mount.

use this command
xedit /etc/fstab &

this will open a window for xedit showing the file called fstab. this is the file that linux looks at to mount drives.

it will look something like this
LABEL=/ / ext2 defaults 1 1
LABEL=/boot /boot ext2 defaults 1 2
/dev/fd0 /mnt/floppy auto noauto,owner 0 0
none /proc proc defaults 0 0
none /dev/pts devpts gid=5,mode=620 0 0
/dev/hda5 swap swap defaults 0 0
/dev/cdrom /mnt/cdrom iso9660 noauto,owner,kudzu,ro 0 0
/dev/hdd4 /mnt/zip250.0 auto noauto,owner,kudzu 0 0

the first part is the original hardware name (i.e. /dev/hdd4) then you will see the human readable name (i.e. /mnt/zip250.0). the "/mnt/zip250.0" is the device that you mount and go to to view the data within. here is the command mount /mnt/zip250.0
it may say that root needs to do this so then you just su into root and then go in.

Add an fstab entry for all desired devices you want to mount and then also add a desktop shortcut.

My shortcommings is being disorganized and having several distros loaded and that I don't mount all partitions. So of course a file I need is always on an unmounted partition.

There is no absolute relationship between the mount point name and device name. A mount point is just a directory somewhere in the filesystem. The process of mounting attaches for example the floppy to the filesystem. It is common to place temporary mounted devices like cdroms etc under the /mnt directory but not all distros do this.

There are a ton of posts on mounting and fstab that you can search for. Also see man pages for mount and fstab.