Ok. Firstly, "affirmative" is literally a confirmation of something being true. In debating, the affirmative team/side is the team/side that agrees with the motion. (The motion is the proposal that you're debating about.) The affirmative case is the case presented by the affirmative side. The other side of the case is "negative".
Now, about the points you want clarified:
1.) This means to state your argument. For example, if the motion is that President Obama's stimulus bill should be passed, your argument, being affirmative may be: "President Obama's stimulus bill must be passed." In debating, it is essential for you to have a strong stance, so you need to use words like "must", rather than words like "should" in your speech. Specifying your standpoint is important because it starts off your side with a strong foundation to work from, as well as letting the adjudicator, floor, and opponents to know exactly what the point you are trying to make is, straight from the get-go.
2.) Specifying the role of the second and third affirmative means to give an outline of what aspects the second and third speakers on your team will talk about. This, along with specifying your case, is kind of like a thesis in an essay.
3.) Introducing your argument on the affirmative case means exactly that: to introduce your argument supporting the motion. Basically, you begin to expand on your "thesis statement".
4.) Reaffirm the affirmative case. In fact, each speaker on the team must to this after proving their evidence. You link the evidence you have presented back to the case. How does the evidence support your argument?
5.) Every debater needs to give "points of information". This just means presenting evidence. Evidence is necessary in order to support your case. As in, you can say "the motion must pass" all you like, but you have to say WHY. The evidence (or "points of information" is the substance of the "why".
I wish your luck on your debate!
