Last year, SpaceX debuted their Falcon Heavy for the first time on February 6th, 2018, carrying Elon's Tesla Roadster as the test payload. The main event of that launch was the successful landing and recovery of the side boosters, which landed nearly simultaneously back at the two concrete landing zones SpaceX had constructed. Since then, the Tesla roadster has completed 3/4ths of its orbit and SpaceX hasn't launched another Falcon Heavy, why is that?
The next scheduled launch of Falcon Heavy was supposed to be STP-2, launching in June of 2018, but got pushed back to next year. Just about 3 months after the debut of Falcon Heavy, SpaceX rolled out their brand new "Block 5" varient of the Falcon 9 which had a ton of new upgrades to the rocket. Block 5 features more thrust, more launch capability, stronger structure of the first and second stage, plus a ton of upgrades to make repid reusibility possible. These upgrades to the rocket's structure and power had to be translated over to the framework of Falcon Heavy.
This years Falcon Heavy has a thrust increase of about 10% as compared to last years launch, so it will be louder and more powerful.
The launch is carrying ArabSat 6A, a high-capacity communications satellite for the Middle East, Africa, and Europe, which will deliver television, radio, internet, and mobile communications.
Falcon Heavy's launch window opens at 6:35pm EDT and extends to 8:32pm EDT, currently SpaceX is targetting a launch at the beginning of the window. It will be launching from historic Launch Complex 39A, located at the Kennedy Space Center in Florida. They plan on landing the side boosters back at Cape Canaveral once again and landing the center core out on the droneship roughly 1000km out, or about 600 miles.