In the upper right corner of the photo (which is what I think you mean by bottom left here) is the space for the hard drive. The cable to connect to the hard drive is still there; any 2.5" SATA hard drive should work. The space is fairly thin, so you should use a drive that's 9.5mm or thinner; but most laptop SATA drives made these days should fit the space.
What's missing from the socket in the middle of the photo is DDR2 RAM (PC2-5300) - one or two sticks. How much RAM your machine can use depends on the generation of the machine; it ranges from 2GB (2x1GB sticks) to 6GB (2+4GB sticks).
The generation/model number is marked on the back. A1150 has a Core Duo CPU; A1211, A1226 and A1260 have Core2 Duo CPUs. We'll be able to give you a lot more guidance once we know what machine we're dealing with.