What is the difference between raise and rise? When and how should I use each one?
"Raise" when used as a verb is transitive: it requires that you have a direct object, a noun of some kind that you are applying the verb to. For example, "I must raise an objection"—"an objection" is the object that the subject (I) is using the verb to act upon.
"Rise" on the other hand, is an intransitive verb: it does not require a direct object; your sentence can be complete without one. "Please rise" is entirely correct and complete.