In Program items, you add all items that relate to the daily program and have a set start and end time.
In Posters, you can add posters or other items that are part of the program, but do not have a start and end time. They can however be part of program items that do have this.
Here you add your sponsors, exhibitors or other organisations that in some way are part of your conference.
Here you add all authors, speakers, moderators, etc. that contribute to your conference. You can link these to program items, for example to set a speaker for a certain presentation.
Classifiers are properties that can be assigned to any of the other data types or to other classifiers to group them. Think about linking a topic to a presentation or secondary topics to main topics.
Places can be indicated on your floor plan. They can be linked to program items or institutions, to show users where these are located.