The israelis illegally occupy land, so the Palestinians fire rockets to tell them to leave. They are crude point and shoot weapons and are unguided, which means they are more symbolic rather than destructive.
The present conflict arose when one such rocket was fired on the 15th April. It landed in an empty field causing no damage, and did not kill or injure anyone.
Israel’s response was an aerial bombardment which has killed hundreds of people, destroyed $millions of property.
Why did Israel make such a disproportionate response now? Well, there has been an inconclusive election that has left Likud without a majority, and Netanyahu is currently in Court facing corruption and fraud charges. Nothing like a good war to distract from domestic problems.