A lectern supports a book from which you read to an audience. The 'lect' bit of the word comes from a latin word for reading. Speakers use them for notes, or just to give them some psychological support or sense of protection, or because holding it while they answer makes them feel confident and presidential. A lectern will usually be around four feet tall or a little less. A podium supports you, to give you a prominent place so you can be seen clearly by your audience and you can see your audience clearly to get feedback. A podium may be only a matter of inches above the general floor level or it may be a foot or two. The 'pod' bit comes from a greek word for feet, same as in tripod. A podium may well have a lectern on it.