First, install one of the zmodem programs from the ports collection (such as one of the two from the comms category, lrzsz or rzsz.
To receive files, start the sending program on the remote end. Then, press enter and type ~C rz (or ~C lrz if you installed lrzsz) to begin receiving them locally.
To send files, start the receiving program on the remote end. Then, press enter and type ~C sz files (or ~C lsz files) to send them to the remote system.