What would a US-Iran war look like?

President Trump today tweeted about a proposed airstrike on three targets in Tehran. He claimed he called off the strike 10 minutes before it was set to happen after he found out about the possible casualties. Iran has since responded, saying they considered shooting down a military plane with 35  people onboard, but decided to attack the unmanned drone instead. That claim has not been verified. After a war of words, sabres are rattled. But what would an actual war with Iran look like?