Learn Russian: Он приготовил вкусное блюдо.

приготовил is the perfective form of the verb. We use it here because the sentence focuses on a single, successfully completed action with a clear result: the delicious dish is finished and ready. If we used the imperfective готовил, it would mean he was in the process of cooking or cooked repeatedly without focusing on the final result.

Why does the verb приготовил end in just -л?

In the past tense, Russian verbs change their endings to match the gender of the subject. Since the subject is он (he, masculine), the verb takes the masculine past tense ending -л. If the subject were она (she), it would be приготовила.

Why didn't вкусное блюдо change its ending, even though it is the direct object?

The phrase вкусное блюдо is the direct object (the thing being cooked), so it is in the accusative case. However, блюдо is an inanimate neuter noun. For inanimate neuter nouns, the accusative case looks exactly like the dictionary form, so neither the noun nor its matching adjective changes its ending here.

Is the verb приготовил related to the word готов (ready)?