Pythagoras describes his background and teachings to the potential buyer.
φέρε δέ: "come now." The imperative of φέρω and ἄγω (often with accompanying δή--see section 12 of this text for an example) are used to emphasize the main action in the rest of the sentence, and in such cases should not be translated literally, since they are acting like particles that add flavor to a sentence (S. 2773). The main action of the sentence is usually expressed as an imperative (S. 1836) or a hortatory subjunctive (S. 1797a), but here φέρε adds urgency or emphasis to a future more vivid conditional.
τί με διδάξει; "what will you teach me?" διδάξει = future mid. 2 sg. > διδάσκω. The middle voice of this verb usually means "to have someone taught," but in late prose and occasionally in poetry, it can function like the active voice (LSJ διδάσκω A). The MSS have διδάξεις but διδάξει is an emendation accepted in some editions, because of the middle form διδάξομαι in the next sentence. The meaning is clear from context even if the exact choice of word here is not.
ἀναμνήσω: ἀναμιμνήσκω, fut. ἀναμνήσω remind, call to mind (+ acc. of person + gen. of thing).
ἐκκλύσας: this is from ἐκκλύζω, "wash out."
καὶ δή: "well …." used to introduce a reply (see S. 2847b) and also to signal a general supposition (S. 1771). Either use works in the context here and perhaps it does both.
νόμισον: aor. act. imperative 2 sing. > νομίζω, "consider, suppose, assume (+ acc./infin.)."
ἐκκεκαθάρθαι: perf. pass. infin. > ἐκκαθαίρω, "purify."
τρόπος: "method." This is a meaning found in philosophical texts starting in the Hellenistic period (LSJ τρόπος VI).
τὸ μὲν πρῶτον: adverbial, "first of all" (S. 1611).
καὶ πέντε ὅλων ἐτέων λαλέειν μηδέν: καί has explanatory force here and so functions like id est (i.e.): "namely, to say nothing for five whole years" (conjunctional or epexegetical καί: S. 2869). The genitive can express the amount of time until an action will happen (S. 1446). The infinitive is here functioning as a nominative verbal noun in apposition to the silence (ἡσυχίη) and speechlessness (ἀφωνίη). The five years of quiet must occur before Pythagoras can make the buyer remember anything of philosophical importance.
ὥρα σοι + infin. = "it is time for you to..." i.e. “you should,” (LSJ ὥρα B.I.3).
τὸν Κροίσου παῖδα: Croesus was a famous king of Lydia, one of whose sons was mute. For the story of Croesus and his sons, see Herodotus, Histories 1.34-45 and 1.85, where the mute son speaks for the first time in order to save his father from a Persian soldier.
λάλος, -ον: talkative, babbling, loquacious, i.e. "a good speaker.”
ἐνασκήσεαι: future mid. 2 sing. indic. > ἐνασκέω, "train or practice in a thing."
κᾆτα: crasis for καὶ εἶτα.
χάριεν: gracefully, elegantly, beautifully. The neut. of this adjective (χᾰρίεις, χρίεσσα, χαρίεν), as Adv., was written χάριεν in the Attic dialect (see LSJ IV).
κᾆτα = καὶ εἶτα (crasis: S. 62 and for the specific dropping of -αι in crasis, see S. 68c).