yes, you can prioritize your tasks in Todoist. To do so, simply right-click on a task and choose one of 4 available priorities (1 being the top priority) from the context menu.
You can also add a priority to a task while adding the task. To do so, type !p1, !p2, !p3 or !p4 within the task name.
Yes, we're listing all features/shortcuts on our help pages. Please click on the question mark icon in the top-right corner on the web-app and you can read the help pages in the "Usage reference" section explaining keyboard shortcuts, text formatting, supported due dates etc.