This is one of the options available on your day off (weekend). Selecting this will assign a lecturer to hold a seminar that will increase all participating units’ skill experience and motivation. Before you can commit to a seminar, you can see the preview of available lecturers and the topics they’ll discuss and the attendees. If you don't like the topics or the possible attendees, you can cancel out of this screen and still select other actions you want for that weekend.
After the seminar, all attendees will earn EXP on the Skills the lecturer covered. If their skill ranked up, they'll also automatically learn the corresponding Ability/Combat Art specific for that skill. Each attendee will also get +50 Motivation at the end of the seminar. This action will take up your entire weekend so think carefully if the attendees will benefit from the seminar.