Pls help!problem about Pc data tranfer to 8051 by serial port using keil C

i am now developing an temperature control project.
As in my project, i need to enter certain varible to the 8051 micro-controller by PC before it start to work itself.

However, i feel difficult to the develpoment the communication program for the communication parts.
how can i find some referance material and simple source code in order to get the starting point of my program.

Pls help and many thx!