Go to Google and use simple search query “Set timer for <time>” as soon as you will press enter timer will start. It is vary easy to use with Stop and reset buttons. It also have sound which will alert you after time is complete. You may disable sound, to do so simply click over sound icon.
You can start timer simply by typing “timer” in search and then you can manually enter time. See above .gif to better understand the working of google timer.