I guess PLS(+) is step, DIR+ is dir, EN+ is en, and all the - are ground.
I think the command signals (step, dir, en) are optoisolated, this means galvanically isolated therefore connectors for each has its own ground. This is useful if you have different power supplies, with different grounds, for example one supply is for motor current (gnd1) and another supply is for the microcontroller (gnd2). But, if you use a *single* supply, you have only one ground, therefore all connectors with (-) minus sign go to a signle ground so you can just connect them together, and on the (+) side you put the normal control signals as you normally would if you only had one pin to connect to.
I think the command signals (step, dir, en) are optoisolated, this means galvanically isolated therefore connectors for each has its own ground. This is useful if you have different power supplies, with different grounds, for example one supply is for motor current (gnd1) and another supply is for the microcontroller (gnd2). But, if you use a *single* supply, you have only one ground, therefore all connectors with (-) minus sign go to a signle ground so you can just connect them together, and on the (+) side you put the normal control signals as you normally would if you only had one pin to connect to.