Gandalf is one of the Order of Wizards who has been sent to Middle-earth to oppose Sauron. Gandalf have been working ceaselessly to counter Sauron's plans to dominate Middle-earth, and he have now set in motion a chain of events that now have involved you, whether you like it or not.
Gandalf have left you some information on the above coordinates. The information will look something like this:
You can then use this formula to get your new coordinates:
N 57 51.[f+g][b+l][d+e]
E 012 26.[h+n][a+c][m+j]
The new coordinates will take you to the main entrance into Mordor - the Black Gate - a great barrier of iron across the gap called Cirith Gorgor, where the Ash Mountains and the Mountains of Shadow meet at the northwestern corner of Mordor. The Black Gate is heavily guarded and it is flanked on either side by the Towers of the Teeth. Hence the Black Gate is too well protected for you being able to get into Mordor without being noticed.
If you approach the Black Gate, be stealthy - there are Uruk-hais living close to your path.
But there is also a lesser-known way into Mordor from the Morgul Vale... A Straight Stair and a Winding Stair leading to a tunnel where the Great Spider Shelob lurks.
You will have to find this way into Mordor and manage to get all the way without waking the the Great Spider Shelob.
Once inside Mordor you will have to meet Gollum - once a hobbit-kind person known as Smeagol. Smeagol committed murder to obtain the One Ring belonging to the Dark Lord Sauron which had been lost when Isildur was slain in the Gladden Fields in the year 2.
Gollum will lead you to your precious.