How to transfer pictures from my iphone to an sd card?

Do i just save iphone pics to my computer then put them on the sd card?

That's the way I would do it. With my camera, I put the SD card and USB drive in the computer at the same time, and copy or move the pix. Does your iphone look like a drive to the computer? If so, direct copy or move can be done.

Move all content from iphone to pc, then use a memory card reader/writer, put sd card in reader/writer, plug into pc and move all iphone content on to it.