+revellerent+ = +re + vello+ = _pluck-away_. If you forget the meaning of +vello+, the supine +vulsum+ through some English derivative--e.g. _re-vulsion_, _con-vulsion_--will probably help you to the root-meaning.
(ii.) _Translation._--This sentence contains four finite verbs. As you read it through, underline the principal verb, clearly +REPERTI SUNT+, and bracket +qui+ to +vulnerarent+. You cannot doubt which verbs to include in your bracket, for +qui+, which is a subordinate conjunction as well as a relative pronoun, serves as a sure signpost. Also +revellerent+ and +vulnerarent+ are joined by +et--et+ to +insilirent+, so your bracket includes all from +qui+ to +vulnerarent+. The commas in the passage will often help you to the beginning and end of a subordinate clause. Now begin with the principal verb +REPERTI SUNT+ and its subject +complures nostri MILITES+, _many of our soldiers were found_.
+qui ... vulnerarent+. This subordinate clause describes, just as an adjective does, _the character_ of these +complures nostri+, so that +qui = tales ut+--i.e. _brave enough to leap upon the phalanxes, and pluck away the shields (of the Germans) and wound them from above_.
+IV.+ +Cum hostium acies a sinistro cornu pulsa atque in fugam conversa esset, a dextro cornu vehementer multitudine suorum nostram aciem premebant.+
√+ac+ = _sharp_ (cf. +ācer+), perhaps thought of as the _edge_ of a sword.
+cornu+ = _horn_; so, figuratively, _the wing of an army_.
(ii.) _Translation._--This sentence contains three finite verbs. Underline +PREMEBANT+, clearly the principal verb, and bracket +cum+ to +conversa esset+. Here the signpost is the subordinate conjunction +cum+. Next find the subject of +premebant+: obviously no word from +a dextro+ to +aciem+ can be the subject; it is implied in +premebant+--i.e. _they_, which as context shows = +Germani+. Now find the object = +nostram aciem+ = _our line_.
Thus you have as the backbone of the whole sentence:--
_They (the Germans) were pressing our line._
All the rest of the sentence will now take its proper place, as in some way modifying the action of +premebant+.
+cum ... conversa esset+ tells us _when_ they were pressing. +a dextro cornu+ „ „ _where_ „ „ +vehementer+ „ „ _how_ „ „ +multitudine suorum+ „ „ _how or why_ „ „