A progress indicator shows that a task is happening or how much of it is done. It is like watching a measuring cup fill while something is being prepared.
For example, a line that fills from left to right can show how much of a file has uploaded. A spinning shape can mean the site is working, even when it cannot tell you exactly how long the task will take.
Choose the kind that matches what the site knows. If the amount is known, show it; if not, simply let people know work is underway. Do not leave the indicator moving after the task has finished.