Then, with gold-coloured contacts of your SIM card facing downwards, just push it into the slot until it reaches the end. It should make a click sound when fully inserted. Remember to position the cut-edge of the SIM card exactly like it’s shown in the picture. NOTE that after you've inserted the SIM, the device has to be rebooted (same when it's taken out).
Based on experience, I DO NOT recommend using a plastic adapter to make an iPhone micro SIM larger as this may jam in the SIM card bay possibly requiring disassembly to remove.