On this motherboard RAM slots are colour-coded, blue for DDR and black for SDR (also well-labelled on the motherboard itself). There are always 2 clips at each end which snap back into place when the RAM stick is pressed-in fully. Can require a bit of pressure to get it, but make sure the RAM is the right way round... (see the notches!).
The photo shows 1 stick of DDR PC2100 RAM in the blue slot (mid-top of picture).