It depends on the verb's ending how you form the imperatives but there are always two* options: an informal ("tu") and a formal ("Lei"). In most cases it is safe to stick to the indicative forms, like in "veni qui" vs. "venga qui", with the formal version of course being third person.
However, for verbs ending in -are, this is somehow reverted. Thus, "scusi" is the formal and "scusa" the informal imperative of "scusare" and you use the third person for second and vice versa.
(* Plus the "let us" type of first person plural imperative which is easily formed by using the corresponding indicative form.)