Warning Messages

I have 5 different C files and i Main.c program separately. In the Project diaglog box i have added all these files.
For Target Options i have selected Large 64kCode ROM size and memory model Large.
And selected output as hex.
Upon building the target file,
I get warning messages.
1. Unresolved external symbol
2. reference made to unresolved external sysmbol
3. ignored for overlay process.
i dont know how to eliminate this messages.
Please help me.

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