I know of two ways to attach multiple flies to a fishing line....
Some do a dropper rig, with one fly at the end of the tippet and two flies are attached on dropper loops, further up on the dropper rig (tippet).
Others just use a uniknot (or similar knot) to attach the fly to the curve of the previous fly on the tippet.
The choice of which way to go, is your decision. ~Parnelli