There's an ATVO municipal bus that runs directly from Piazzale Roma to Jesolo, though you should take the scenic route by hopping an ACTV ferry from Venice proper to Punta Sabbioni. From there, the ATVO number 5 bus will take you up to Jesolo. The ferry from Venice departs from the jetty in front of the Santa Maria Della Pieta on Riva degli Schiavoni, close to Venice's famous Bridge of Sighs. You can walk there from Piazzale Roma or take a water bus.