In order to manufacture your board, you need to take the circuit in Multisim and layout your design (that is what Ultiboard is for). Once you have finished the layout phase, you send the gerber, drill, and centroid files to your manufacturer (plus anything else they may ask for). Multisim cannot export to .pcb format - I believe this is their own format - but Ultiboard can export all of the files you will need.
