In the Marvel Universe on Earth-616, Galactus used a device or series of devices called the Elemental Converter. This device refines the life-force of a planet and makes it able to be integrated into his cosmic armor which sustains and energizes him.
He does not need the Elemental Converter, but it makes the process smoother and more efficient, maximizing the life force harvested.
In the cinematic Fantastic Four: The Rise of the Silver Surfer, the Surfer is preparing the landing sites for these devices by boring giant holes into the Earth. The cinematic Galactus, while unseen, would be by the standards of his comic counterpart to be a bit impatient having the Surfer choose and prepare the sites before his arrival.
This just in: In a parallel universe, Marvel Earth-111 was attacked by their universe's Galactus. Footage from a Russian news camera caught this shot of his Elemental Converter being assembled over Moscow before being consumed. It was brought back to our Earth by Ben Grimm of Fantastic Four fame.
Earth-111 Galactus setting up his Elemental Converter
More Detailed Answer:
In the Marvel Universe, Galactus is also known as the Devourer of Worlds. He was created by Stan Lee and Jack "King" Kirby. In his origin story we learn he is the last survivor of the previous universe, from the super-advanced world of Taa and survived due to interactions with the primal force of the Universe (possibly the Phoenix Force).
Death of the previous universe, and the origin of Galactus
After his survival he seen, by a Watcher, reconstituting himself with unknown energies and being embodied in an armor which regulates his life force. His body is now composed of an unknown and incredibly power energy he calls, the Power Cosmic, which he will later distribute a tiny fragment of the power to his Heralds, beings tasked with finding him life energy to consume.
Galactus only uses a few machines, one of them is his World Ship Taa and later Taa 2. It is a ship larger than a planet and houses whatever creature comforts and technology a space god could possibly need.
Taa, the World Ship of Galactus
- He also uses a technology called the Elemental Converter. This device gathers and purifies the life force of a planet for Galactus' easy consumption. It also refines the life-force enabling Galactus to maximize its potency and increasing his time between feeding. There are very few images of the Elemental Converter since worlds who are exposed to it, are rarely seen or heard from again. We have a picture from a confrontation between Galactus and the Phoenix Force. The Elemental Converter is the machine Galactus is standing over in the lower panel.
Galactus battles the Phoenix and loses the battle but scores a moral victory.
Galactus does not NEED to use the Elemental Converter. He can simply absorb the life force of a planet directly, but this is both less elegant, resulting in the physical destruction of the planet and less efficient, wasting valuable life force energy. Direct absorption is thus less desirable from Galactus' perspective.
In the movie Fantastic Four: Rise of the Silver Surfer, Galactus has only one Herald, Norrin Radd, the Silver Surfer. The holes being drilled in the Earth by the Silver Surfer were to be placement points for the Elemental Converter. This device is seen in the comics in various iterations being created by Galactus or on occasion by his Heralds.
In the series Finale of the Avengers: Earth's Mightiest Heroes, Galactus sends four Heralds/Constructs to prepare the Earth for his arrival and each Herald creates an Elemental Converter before being confronted by the various Avenger teams.