if you've got a tgz / tar.gz archive, you can extract its contents wherever you wish - i tend to use /usr/local/src, but you could use your /home directory instead. if you do use eg. /usr/local/src, you may need to be root to copy stuff there.
anyway, wherever you decide, the src folder will be within the folder containing the files you extracted. now, if you extracted the archive as the root user, you'll need to remain root when you run 'make', or you may well get errors as you describe..
the object of the exercise is to compile the source code in the src folder, which will result in a kernel module (bcm5700.o) which you can then load. you'll almost certainly need to have the kernel source installed on your machine - should be available on your distro CDs. but just give compilation a try first - you might be good to go already..
have another go and post back with progress