Since this word has okurigana (hiragana attached to the kanji) you know that it's probably going to be the kun'yomi reading.
Lucky for you, the kanji readings for transitive and intransitive verbs are almost always the same. Once you learn one, you know them both! This reading is the same as 始める.
What time does the movie start?
A fierce economic war between America and China has begun.
The sound of the rifle means the pie eating contest has started.