In Mortal Kombat X, combos are quite difficult to pull out, because you first need to make sure that the opener (the initial blow) connected. One of the methods that you can use is jump and use the punch twice so, after you land, you can hit the opponent again and not let them defend, thanks to which the attack can be continued. After the first blow, the opponent will receive a considerable delay to the block. To perform a combo, timing is crucial. To connect individual attacks into a chain, it is necessary to stat the NEXT move BEFORE the previous one ends. For example, in the case of Scorpion's punch, punch, spear (2,2,<,>+2) combo, you need to perform the spear combination BEFORE the second punch connects. The best way to master this system is to practice it in the training mode. If you feel the appropriate rhythm and figure things out, it is going to be much easier.
The same goes for juggling - if you knock the opponent into the air (Neutral jump + 1), you can do with them, whatever you want. You then execute your combo on the inert opponent for free. It is worth pointing out that after you execute the juggle, you can grab the opponent in mid-air and perform a throw (if the current variant of your character allows that).
All of the attacks with the, so called, Capture State (immobilizing, dragging, etc.) are a bit different, when you use them again. This is to prevent you from dragging the opponent to yourself, over and over again, in the way that prevents them from doing anything. This way, you could form an endless combo, which would not make much sense. In such a case, e.g. if you use Scorpion's spear again, before the opponent regains control, your character uses high punch, which tosses the opponent into the center of the arena.