Apple MacBook (13-inch, Aluminum, Late 2008) - Manual (Page 46)

46 Chapter 3 Boost Your MacBook
7 Insert the new memory module in the slot:
a Align the notch on the gold edge of the module with the notch in the lower memory
slot.
b Tilt the card and push the memory into the slot.
c Use two fingers with firm, even pressure to push down on the memory module.
You should hear a click when the memory is inserted correctly.
d Repeat to install an additional memory module in the top slot. Press down on the
module to make sure it is level.