What is in the RAR? (did you open it with a program like 7zip or WinRAR?)
Is it a patch (an IPS file)? Or did you find a prepatched ROM somewhere (a .gb file. If it is, DON'T say where it's from). Your filename suggests it is a prepatched ROM.
If it's a patch, you need an original Pokemon Blue ROM, and a patching program like LunarIPS.
If it's a ROM, you just use the program (7zip/WinRAR) to uncompress the file, and then run the uncompressed file with VBA.