When we are talking to a group of people for example a students or viewers,
Is it best to use the plural when giving a command?
Look at your fliers?(the audience each has one flier since there are many people holding so there are more than one?)
Look at your flier(refer to one person and everyone follow)
Should hand be plural or singular?
Raise your hand(s) ( usually one person raise only one hand, but there is an audience which means many people. All together they have many)
At there end of the explanation I want to confirm if the audience understand?
Should the sentence be in past or present?
Does everyone understand?
Did everyone understand?
To understand one must be absorb the information which mean its has to be in the past. But I have heard both versions.
 your flier
 Raise your hand.
 Did everyone understand?
Good luck on your presentation.