Using a temperature sensor I2C. Where do registers come into code?

Ok then two more things to clarify from your repsonses, but I think it's becoming clear.

Where you've put 0x00 I'll put 0000000 (the register pointer for ambient temp register?)

I want all of the first byte and to "add" the first bit of the second byte on the end?

What's the function called to join the two pieces of data after I've done the bit shifting?