Learn German: Ich war gestern sehr traurig.

war is the simple past tense of sein (to be) for ich (I). While Ich bin means 'I am', Ich war means 'I was'. You will use the simple past tense a lot for the verbs 'to be' and 'to have' to talk about the past.

Why is gestern placed right after the verb instead of at the end of the sentence like in English?

In German, time words like gestern (yesterday) usually come much earlier in the sentence than they do in English. A good rule of thumb is that time information comes right after the main verb.

Does the adjective traurig need any special endings here?

No. When an adjective is used with the verb 'to be' to describe the subject (like 'I was sad' or 'the dog is brown'), it does not change. It stays exactly in its basic dictionary form.

How should I pronounce the -ig at the end of traurig?

In standard German, the -ig ending is pronounced exactly like the 'ch' in Ich. So traurig sounds similar to 'trou-rich'. In some southern regions of Germany and Austria, you might hear it pronounced with a hard 'k' or 'g' sound, but the 'ch' sound is the standard.