If you pick the "all active and inactive" options, it will send that job to all the agent on that agentgroup... and as such each agent (offline or online) will try to run it it at the same time then (unless you have max parallel set).. if the agent is offline at the time, from what I remember... that job would go into a "waiting for host" status until that agent is available...
Not sure if there something you are looking to do with it or just trying to learn how these work but I recommend playing/trying it out.