How the time slows down? In thought experiment of special theory of relativity in which two mirrors are used how the time gets slow for moving person?

Question

If experiment is observed from stationery frame of reference then light travels more distance than frame of reference of mirrors so to keep speed constant time for stationery frame of reference should be increased which maybe means that same event is happening slower in stationery frame because completion of same event is taking more time when viewed from that frame because distance covered has increased. Then why we say that in moving frame time passes slowly?

Answer 1

We don't exactly say what you just said.

We say; if you're an observer moving at some speed, your time according to you will pass normally so you won't notice your own clock running slower or faster, but when you measured time between some events (e.g. how other person's clock ticks) this time will be seen as passing slowly.

Additionally, if a stationary observer watches how your clock ticks (you are moving at some speed as in the previous example), s/he will see as if it ticks at a slower rate. This is the whole point of relativity.