UNRESOLVED EXTERNAL SYMBOLS

 UNRESOLVED EXTERNAL SYMBOLS

I am really new to 8051 programming, but my first program gives this warning: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?C_START MODULE: STARTUP.obj (?C_STARTUP)
what shuld i do?

 RE: what should i do?

You should start by copying the text of the warning into the 'Search' box to see what help already exists on the subject...

 RE: UNRESOLVED EXTERNAL SYMBOLS

You are probably declaring the 'unresolved symbol' in one module and using it in another.

 RE: UNRESOLVED EXTERNAL SYMBOLS

but my first program gives this warning:

First, no, that's not a warning. It's an error message.

Second, you're using the wrong program as a first one. Your first program should be the one from the tutorial, built exactly like the tutorial tells you to. Odds are you'll find your mistake yourself, once you've complete the tutorial.