Unless they are delivering a car, no-one drives across Europe to get to Malta. There are car ferry services from some Italian ports but the cost/hassle against the option of cheap flights and the cheap cost of car hire on the island makes this a non-starter for conventional holidaymakers.

Getting to Valletta is relatively easy as it is the transport hub of the island and all main roads are signposted. Unless you are resident here (in which case ask your host about parking) park outside the walls in one of the marked car parks. Valletta's streets are steep and narrow and much of it is now pedestrianised.