When implying knowledge rather than the presence or absence of an impediment, use SAVOIR - not POUVOIR. SAVOIR is the French equivalent of the verb CAN in English.
Je NE SAIS PAS conduire. I CAN'T drive.(That is, I never learned.)
Je NE PEUX PAS conduire. I CAN'T drive.(My car is in the shop.)
能理解。。。
