Learn English – the difference between sugar cane and cane sugar

The verb lay is transitive.

You lay something on the table.

The verb lie is intransitive.

You lie on the table when you are operated upon.

The confusion comes because the past tense of lie is lay:

He lay on the table for two hours before he was operated upon.

Few native speakers get this right. Most people would say, "He laid on the table for two hours." Bill Clinton constantly made this mistake in speeches.

"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.