To hold a lecture in SL it can be helpful to acquire a slide viewer. Slide viewers provide the lecturer with the opportunity to introduce additional information to the audience.  Viewers can have different names depending on the design. They are obtainable many places in
SL .One place you can acquire a free slide viewer is given in this SLURL  Educator’s Corner

Through an avatar, a lecturer can be represented in very many different ways. In SL as in RL it is not wise to judge a book by its cover. This is in fact one of the lessons which can be
learnt in SL and brought with you back to RL.  People can have various reasons
for their choice of avatar, and netiquette dictates that one doesn’t make any
kind of issue out of it! It can be an advantage to design the auditorium or room for a lecture without walls and doors,  as this affords easier access and visibility for all participants.

MICA – Meta Institute for Computational Astrophysics

It is important to note that low ceilings and small rooms make it very difficult
for participants to get the “big picture”, or the atmosphere of an actual educational institution. Creating the proper physical structure helps to create the proper atmosphere for a learning environment. The lecturer will most often be using voice. It is advisable for all guest/ students at a lecture to have their microphones turned off!  Guests, students or the audience can chat in text while the lecturer speaks. The lecturer can choose to ignore this chat or,  to benefit from the ideas and reflections of the audience. The audience can ask answer questions through the chat and thereby through active participation share their knowledge and be part its creation.

How to get your PowerPoint presentation into Second Life.