Tokens are often used in web APIs, where you use one function first to authenticate in some way. This function can do various things like check user/password agains a database or perhaps validate a certificate and returns a token that you use later when calling other service functions. The other service functions can then do a much simpler check to see if the token is ok before serving the requests.
Um, if that is a video then presumably it tells you what to do, at least in a general sense. How about you use the information you have to do as much as you can and then ask us about specific issues? If you're talking about using a specific hardware device designed for authentication then visit the supplier's web site and see what developer resources they provide.