The jumper settings are best found in driver IC documentation. Or perhaps try pololu site, if thats what you use then their site also have good documentation. There are 2-3 lines for each driver that set the microstep mode, if the uC would have to set that for 4-5 drivers, then would need to use up to ~12-15 digital lines, which would be quite a waste. Thats why its simpler to just set them manually.
The uC sends a pulse command that tells the driver to make a move. What kind of move that is, depends on what stepping mode is set on driver chip. If driver is set in full step, a move means 1 step, and again if driver is set in 1/4 microstep then a move means 1/4 of a full step. Hence in 1/4 mode it would need 4 times more pulse commands for same distance. To get the number you need to put in config.h, you can take the number of moves required for a complete revolution and relate that to the circumference of pulley you use. If a full rotation means 200 steps them it also means 800 microsteps of 1/4 etc. Also a full rotation means the circumference of the belt and pulley, e.g. for a T5 pulley with 10 teeths that is 5mm*10teeths =50mm of linear motion generated by a rotation. Equate the full rotation in microsteps with how many mm is a full rotation and get the number of pulse commands you need to send for 1mm of linear displacement.
The uC sends a pulse command that tells the driver to make a move. What kind of move that is, depends on what stepping mode is set on driver chip. If driver is set in full step, a move means 1 step, and again if driver is set in 1/4 microstep then a move means 1/4 of a full step. Hence in 1/4 mode it would need 4 times more pulse commands for same distance. To get the number you need to put in config.h, you can take the number of moves required for a complete revolution and relate that to the circumference of pulley you use. If a full rotation means 200 steps them it also means 800 microsteps of 1/4 etc. Also a full rotation means the circumference of the belt and pulley, e.g. for a T5 pulley with 10 teeths that is 5mm*10teeths =50mm of linear motion generated by a rotation. Equate the full rotation in microsteps with how many mm is a full rotation and get the number of pulse commands you need to send for 1mm of linear displacement.