Time dilation means that two observers can measure different amounts of time between the same events. Interstellar’s “one hour equals several years” is a cinematic starting point for the question. The linked video then discusses how relativity connects time with motion and gravitational fields.
What to separate from the film’s plot
Relativistic effects have been measured and must be calculated for the specific conditions of motion and position. They do not mean that everyone experiences time slowing down. NASA explains that relativity’s effects on clock rates and frequencies matter for GPS (NASA Goddard: Relativity and GPS).
This is an introductory explanation, not a calculation of a time difference for a real-world scenario.