calling C from Assembly

I am trying to learn to call some C floating point routines from Assembly.
I am quite proficient in writing Assembly programs which | have done commercially for many years.
I have read the <> page but can make no sense of it
Basically where is what to be done?
For example what does "You can then use the src file as a template to...."
And " must also include the EXTRN directive for the function, eg: EXTRN CODE (_foo)"
I include it where? Will the final project be an assembly project or a C project?
I have written my own Assy routines for +-x/ in Floating point but now need some Sin/Cos/log functions. Hence the need for C. Which I hate.
I found that it is not possible to use the #pragma src is directed and I have to assemble the file twice.
Can some kind person please help by, say, pointing to some page where I can begin to understand Keil C language conventions. The Keil Documents do not give a place where I can find the start of a thread to unravel. Every explanation points to another explanation in another place. I do know C/C++ but not segment controls much.
Thanks for the help

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