Samsung Galaxy S5 Quick Start Manual page 2

Once the cards are both installed, line up the metal contacts
of the battery with the pins inside the battery compartment,
press the battery against the contacts and push it down into
the battery compartment. When the battery is sitting
comfortably, place the phone's back cover on to the rear of
the handset and apply pressure around the edges to secure
the protective cover.
If you needed a new sim card, you will have received a triple
sim card pack. You'll need to pop out the appropriate sim
card that is needed for your Samsung Galaxy S5 Mini.
Samsung Galaxy S5 Mini uses a Micro sim card.