The event organisers officially open the event. They would explain what the event is for, maybe detail the theme of the current edition, definitely introduce the organisation team (committee) and thank them for their work and finally try to engage all attendees in the event. It is good to allow for a few notes on housekeeping and emphasise event highlights (for instance a banquet or dinner or other social events). If the event had sponsors or special contributors introduce them here as well.
The event organisers officially close the event. There might be a best paper award (regular paper, short paper, poster and/or student paper), definitely a positive closure of the event (don't forget to thank everyone: speaker, audience and attendees, organisers, keynote speakers, sponsors). If known at this stage, provide information on the next edition of the event or at least indicate when it will happen and how the attendees can get further information about it.
This is a longer talk with a broader topic that needs to be interesting for all potential attendees of the event. The speaker needs to be carefully selected to draw people into the session (i.e. have some reputation that interests the attendees). The topic then depends very much on the speaker of course. Important is also to invite someone who is a good speaker! And don't forget to a gift got her or him after the session! On multi-day events, each day can start with a keynote. Single day event quite often start with a keynote, but from my experience it is usually better to have the keynote later in the morning (attendees might come later, other people might just walk-in but not for an early morning session).
Regular Paper Session
A few papers, each given the same time to be presented and each presentation followed by a question and answer round. Requires a session chair, who optimally introduces the session providing an overview of the papers and presentations, introduces the individual speakers and then moderates the Q&A round.
Regular Session with Panel
Similar to the regular paper session, but without the Q&A immediately after presentation. Instead, invite all presenters into a panel with the session chair as moderator and then treat every question as a question to the panel. This requires to make sure that papers in the same session are somewhat related, make sure the moderator and the audience understand this relationship and carefully steer the discussions.
Regular Paper Session with Concise Presentation
A regular paper session that distinguishes between full papers (then long presentations) and concise or short papers (then shorter presentations). This mix allows all accepted papers to present, but ranks them. Be careful not to have too many speakers, otherwise the audience might get confused if the session is too long.
A session dedicated to demonstrations, i.e. practical showcases of research. Usually organised like a trade fair, with an open area where people can walk around and watch and listen to what is on offer. Can be combined with a reception (some drinks and small snacks), to bring people in and keep them happy. If you organise one, be careful not to overdo on the drinks yourself. Another option is to run the demonstration session like a regular paper session. However the interactions will be limited and I think this is only useful with a rather small audience.
A group of invited panelists discusses their opinions for a given topic with the audience. The topic needs to be prepared well in advance, and usually each panelist will prepare for a short opening statement. Important for an interesting panel is to invite people who do not agree on everything, can openly and fairly discuss controversial opinions and obviously have a string opinion on the given topic. The moderator needs to be prepared for all eventualities, and should at the end find a satisfying conclusion of the discussion. Important is to keep the initial statements short and allow for plenty of discussion time.
Distinguished Expert's Panel
Same as a panel, but with really distinguished experts in the field.
Invited Paper session
A session that includes papers that have been specifically invited by the programme chairs. This is done to cover certain parts of the agenda or to cover certain aspects that are important but might not have been addressed by regular submissions. The invited papers might be in the proceedings, if so they are usually specially marked as invited.