j.4x (in combos) refers typically to an air dash forward. Although for movement purposes, you can go backwards with it too.
Notations like j.3acd refer to the buttons you have to push. Since in curse, you have to push a button to summon a bug, and the general direction that you hold the stick (forwards/backwards) dictates where the bug is summoned. So you need to be holding forward to summon the bugs in the corner, which explains the 3 part of the notation. What you are trying to do is dive > a bug hits > c bug hits > d bug hits. You do not land and perform 5c and 5d. press c and d while doing j.3a.
Same for command teleports.