Learn Turkish: Sen keçilere ot veriyordun. - You were giving grass to the goats.

This is the past continuous tense, which you use for ongoing actions in the past. It is built by combining the continuous suffix -iyor (doing) with the past tense suffix -du (was) and the personal ending -n (you). So, ver-iyor-du-n translates to "give-ing-was-you", or "you were giving".

Why does keçi (goat) become keçilere here?

We add the plural suffix -ler to make it "goats", followed by the dative case suffix -e which means "to" or "towards". The verb vermek (to give) needs this dative ending for the receiver of the action, showing that you are giving grass "to" the goats (keçiler-e).

Why is ot (grass) in its plain form instead of taking an object suffix like otu?

In Turkish, you only use the accusative case suffix (which would make it otu) when you are talking about a specific direct object, like "the grass". Because this sentence is about giving general, non-specific grass, ot stays in its plain dictionary form.

Is the word Sen required at the beginning of the sentence?