If you have your manual, you should have info on how to set the feed rate. My dad's late has 2 sets of gears. One for Metric Threads and one for imperial units. There are some excellent videos on Youtube showing the process of cutting threads.
Some carriages have the option to lock the carriage in place and then the lead screw can be shifted to drive the slide instead. This is usefull if you wish to thread a new chuck part with spiral threads for the chuck teeth, or simply produce a very nice finish on the end of a piece.
My dad's lathe has this gearbox on the end of the leadscrew to set the leadscrew rate in relation to the chuck. The two gearboxes are cascaded so very low rates are possible for a fine finish or relatively fast for cutting threads.
On my dad's late which has a carriage almost exactly like this one, the far right lever engauges or disengages the drive. The locking 3 positon lever next to it places the carriage drive in forward, nutral, or reverse, so right and left hand threads can be cut. The bottom weighted lever engages the carriage brake. The 2nd wheel behind the main cross slide wheel engauges the drive to the cross slide. The dial indicator with the gear on the bottom is used to make a double helix gear. Use the same positon when returning the carriage to the beginning of your cut to cut the same groove deeper. Use it 180 out to cut the second helix if you are going to cut one.
