You can connect them under Settings/Automatic Tracking in Lifesum. You find that option by clicking on Profile at the bottom in the tab bar in the Diary and then on the gear symbol on the next page.
And of course, there is also the option to connect with Google Fit in order to calculate just steps with the built-in phone tracker.
Also these options can be connected under Settings/Automatic Tracking. In order to use Google Fit, please download it from GooglePlay.