I never knew the following:

"Follow the Drinking Gourd" is a coded song that gives the route for an escape from Alabama and Mississippi. Of all the routes out of the Deep South, this is the only one for which the details survive. The route instructions were given to slaves by an old man named Peg Leg Joe. Working as an itinerant carpenter, he spent winters in the South, moving from plantation to plantation, teaching slaves this escape route. Unfortunately, we know nothing more about Peg Leg Joe.

The song and its translation are as follows:
When the sun comes back and the first quail calls,
Follow the Drinking Gourd.
For the old man is waiting for to carry you to freedom,
If you follow the Drinking Gourd.
"When the sun comes back" means winter and spring when the angle of the sun above the horizon at noon is getting higher each day. Quail are migratory birds which winter in the South. The Drinking Gourd is the Big Dipper. The old man is Peg Leg Joe. The verse tells slaves to leave in the winter and walk towards the Drinking Gourd. Eventually they will meet a guide who will escort them for the remainder of the trip.

Most escapees had to cross the Ohio River which is too wide and too swift to swim. The Railroad struggled with the problem of how to get escapees across, and with experience, came to believe the best crossing time was winter. Then the river was frozen, and escapees could walk across on the ice. Since it took most escapees a year to travel from the South to the Ohio, the Railroad urged slaves to start their trip in winter in order to be at the Ohio River the next winter.

The river bank makes a very good road,
The dead trees show you the way,
Left foot, peg foot, traveling on
Follow the Drinking Gourd.
This verse taught slaves to follow the bank of the Tombigbee River north looking for dead trees that were marked with drawings of a left foot and a peg foot. The markings distinguished the Tombigbee from other north-south rivers that flow into it.

The river ends between two hills,
Follow the Drinking Gourd.
There's another river on the other side,
Follow the Drinking Gourd.
These words told the slaves that when they reached the headwaters of the Tombigbee, they were to continue north over the hills until they met another river. Then they were to travel north along the new river which is the Tennessee River. A number of the southern escape routes converged on the Tennessee.

Where the great big river meets the little river,
Follow the Drinking Gourd.
For the old man is awaiting to carry you to freedom if you
follow the Drinking Gourd.
This verse told the slaves the Tennessee joined another river. They were to cross that river (which is the Ohio River), and on the north bank, meet a guide from the Underground Railroad.

From

http://www.madison.k12.wi.us/planetarium/ftdg1.htm