You can do both. The SD card method is the easiest. You can create waypoints in Humminbird PC, upload them to the SD card, then put the card in the unit. The unit will automatically recognise if there are new waypoints and upload them to memory.
The PC connection is also pretty easy, but you have to remove your unit and make all the connections with power, usb/serial, etc. Again, you use Humminbird PC to create and upload the waypoints right to the unit.
Robert