It depends on what you mean by seminar - it sounds like what you'd like to organize is simply a reading group, in which case all you would need to do is recruit some students (via email or otherwise) and set a date and time to meet. If people are interested in the topic, they'll come because it requires a low commitment. Organizing such a thing requires no special knowledge on your part, just do it.
In my department, we have several graduate student seminars that are slightly more structured, but still fairly casual. Every week, a student presents some work, either to practice for an upcoming conference, defense, or just to talk about a subject they recently learned about. These are usually organized by a second or third year student, mostly because they need to coordinate a particular person to talk each week, and this is difficult to do if you don't know anyone and they don't know you - it's easier to persuade someone to give a talk if you know them. For this type of seminar, I would recommend not trying to organize until you've seen how it is run.