Do you want to easily time how long it takes you to solve the Rubik's Cube?
There are several websites for that. My favourite is csTimer, the timer used by most speedcubers.
Just press the space bar! It is free, works in the browser, generates official-style scrambles and saves all your times, averages and statistics.
Other online timers
Besides csTimer, there are other online timers for the Rubik's Cube, such as Cube Timer or Ruwix.
Buy a physical timer
Online timers have the advantage of always being with you, and they are free. But if you want to be more professional and get used to competition timers, you can buy a (physical) Rubik's Cube timer, often with free shipping.