You can track time on your tasks. To do this you first need to activate time tracking for your project. Click on the info icon next to your project name, click manage and switch to the tab "Features" to activate time tracking.
You can now track the time spent on each task from within the task detail dialog. Simply click on the timer icon in the right side bar to start the tracking. Click on the icon again when you stop working on the task. Your time slips will show up in the Time Tracking register of the project dialog, where you can review and edit them.
On the top right of your dashboard you will now find a timer button that opens a popover with an overview of all your time slips.