Is this the sort of thing you mean?
http://www.ontrackplant.com/photo/75407
Simply put the machine works along the track either working to a previously inputted design on the built in computer system or it has done its own measuring and working to the results puts the track to the best line for the ruling speed limit.
The clamps underneath grip the rails and lift them and slew them as required then the tamping tools squeeze and vibrate the ballast to hold the sleepers in the required position.. the process is then repeated over and over again.
Some machines do 1 sleeper at a time others can do up to 3 sleepers.
There are other machines that may also be seen such as:-
Regulators that profile the ballast.
Stoneblowers similar to tampers but they inject measured amounts of chippings under the sleepers instead of packing ballast.
If you go to the home page of the website for the photo there is much more to see.