The best way to start off learning how to write C code is to get yourself a course for that purpose. You won't get that here, so don't ask.
However, if you use Google or similar you can find some real usefull on-line courses on the Internet. A better option would be to go to a bookshop and see what they have in store. There are actually quite a number of books available that could get you started learning how to program in C in combination with teaching the basics of the 8052. Some even have a free evaluation copy of the Keil IDE included on a CD, so your couple-of-bucks investment may be absolutely worthwhile.