First of all, make sure that you have a Sneaker in your inventory. If you don't have it yet, check out this guide for more information.

Yay, you've got your Gear! Now you just have to put the Sneaker or Headset, or both for even better results, on and press the following buttons:

To start the run:

Press the 'Start Run' button on the main screen,

To pause the run:

Press the '⏸' button in the left bottom corner,

To finish the run:

Press the '⏹' button in the left bottom corner, right next to the '⏸' button.