the main purpose of timelapse photography is to create a series of images over time which can then be recompiled into a movie format where time appears to have been sped up
it is also used in astrophotography to create multiple exposures of the same subject which are then “stacked” on top of each other to build up a image to bring out more detail in dim subjects such as deep sky nebulae and glaxies
traditionally, photographers resorted to various methods of achieving this:
manually pressing the shutter release for each shot
using a cable remote control device with computerised algorithm to act as an intervalometer
using a laptop connected via a USB cable to act as a remote control device
using a smartphone via a special cable from the headphone socket to act as a triggering device (eg. Trigger Trap for iOS)
using a smartphone via WiFi to act as a remote device