A computer is a mechanical device that is used to process information that has been entered into it and to display the results through an output device like a printer or a video monitor. In modern times, the term "computer" is mostly used for personal computer systems that are used for a variety of functions, and can also be used for a handheld device called a tablet.
Chang Wong is adept with computers. He uses his technical knowledge to understand the Global Community computer system and its security to alter its databases to conceal Tribulation Force activity, but Chang Wong had to be a mole in the Global Community computer department who received that opportunity because he received the mark of loyalty against his will. Naomi Tiberias is also an expert on computers who can also break into the Global Community security system. That episode made Chang Wong anxious because it made him think that the Global Community may be on to him.
Donny Moore owned a computer store that provided high-end laptops to the Tribulation Force. His store also sold Judd Thompson Sr. a top-of-the-line computer before the Rapture that Judd Thompson Jr. used after the Rapture to print The Underground newspaper.
In Left Behind: The Kids, Jim Dekker was able to program "personal digital organizers" to be able to play a program called "The Cube" that presents the gospel through a three-dimensional volumetric projection. Dekker had found a truckload of personal digital organizers. Jim Dekker was also able to defeat an attempt by Global Community hackers to corrupt the program of The Cube.
Computer technology of various forms exist in the Left Behind series. There is a mention of a supercomputer called the Beast, but nothing else has been made of it.