Learn Turkish: Lokanta çok kalabalıktı, boş masa yoktu. - The restaurant was very crowded, there was no empty table.

The past tense ending for nouns and adjectives is usually -dı, -di, -du, or -dü. However, because kalabalık (crowded) ends with a hard consonant (k), the d changes to a t to make it easier to say. The vowel stays ı to follow vowel harmony, giving us kalabalıktı.

How do you say "there wasn't" in Turkish? Is that what yoktu means?

Exactly! You already know yok means "there is not" or "does not exist". To put it in the past tense ("there wasn't"), we just add the past ending. Because yok ends in a hard consonant (k) and its last vowel is o, the ending follows vowel harmony and consonant mutation to become -tu.

The English translation says "there was no empty table". Why isn't there a Turkish word for "a" or "any" here?

You can add hiç (any) or bir (a/an) for emphasis, but you do not have to. In Turkish, simply saying boş masa yoktu is the most natural, standard way to express "there were no empty tables" or "there was no empty table" in a general sense.

Can I use ve (and) instead of a comma to connect these two thoughts?