Many people are wondering how to install SD Card on the S5. Similar to the Note 3 all you have to do to install an SD card is to insert it on top of the Sim Card slot. Samsung has sort of combined the SD Card and Sim Card slots for convenience and to save space. Some people don’t like the SD card being in the same location as the Sim Card, but it makes total sense that Samsung did this. As phones get slimmer some sacrifices must be made.
You could also read Android Central article that goes into depth on installing the battery, sim and SD Card.