Most people are aware that Hebrew verbs come from three-letter roots. Each root is conjugated in the 8 dimensions of person, gender,plurality, tense, activity, modality, direct-object, and prepositional connective. For example the root Shin Mem Resh means to watch. The conjugations Shin-Mem-Resh-Tauv-Yud and Nun-Shin-Mem-Resh-Nun-Vav mean I watched and we were watched respectively.

The rules for Hebrew grammar are carefully described in many modern books and are well known. Rashi will sometimes comment when a verse is using a rare conjugation of an odd grammatical form.

When presenting grammatical Rashis my favorite reference is the appendix in volume 5 of the Ibn Shoshan dictionary. This very short appendix lists most conjugations.

Verse Ex29-01a discussing the consecration offering of the Priests states And this is the thing that thou shalt do unto them to hallow them, to minister unto Me in the priest's office: take one young bullock and two rams without blemish. Rashi translates the Biblical word Lamed-Kuph-Ceth as coming from the Biblical root Lamed-Kuph-Ceth which means to take. We have conveniently embedded the Rashi translation in the translation of the verse. The closet conjugation rule governing this Biblical word may be found by using table(s) 1 in the Ibn Shoshan dictionary for the Command mode

Advanced Rashi: Rashi literally states We find two command forms for verbs whose first letter is Lamed: The two forms are Lamed-Kuph-Ceth and Kuph-Ceth. Both forms are a command conjugation meaning take. So Rashi is simply pointing out that there are two conjugations to the command form of Lamed-2-3 roots. Although this fact can be looked up in modern grammar books, such books were not present in Rashi's time. In fact even many modern grammar books will only give one form and not mention alternate forms.