DLL injection Guide
DLL injection Win8
DLL injection is not possible with Modern UI on Windows 8, you can read more here: DLL Injection Windows 8.
DLL injection high level overview
DLL injection works when you inject a DLL into a 3rd party process and then you change its internal functions using either code hook/detours or replacing the IAT tables. There are libraries that use driver to perform the hook, but they require admin.
When to use DLL injection?
DLL injection is the only method that doesn’t require admin to use if you want to do any sort of network redirection.
When not to use DLL injection?
First thing to make sure is which detour library you are using, MS has a free one which can be used only for free apps, the 64bit version requires the license (you need different DLLs for 32bit and 64bit DLL), Also it’s not possible to inject to all processes, some will have active protection against it.
The biggest draw back is that some games will detect that as an attempt to bot, and will terminate the gamer account.