Hi,
no context?
PSC? I guess prescaler
ARR?
T_CLK? I guess period time of a clock. Which clock?
Usually a timer is a counter. (true for most counters in most microcontrollers)
* So you have a counter input frequency (F_cnt)
* and you have an integer value when the timer "times out" (TO_val)
t_timeout = TO_val / F_cnt.
The datasheet should give sufficient information.
Also I guess there are STM tutorials for timers (even videos)
And there may be online calculators.
Klaus