Go to the Inbox (1) and add a Task "Prepare Meeting with George" (2) and a Task "Prepare Meeting with CEO" (3).
Our "Meeting with George" is important for us, so we want to give it a higher priority. Priorities are displayed in Organize as blue dots below the checkbox for each task. Three empty dots for Tasks with low priority, one filled for Tasks with normal priority, two for medium and three for high priority.
To change the priority just click on the dots (1). With every click the priority goes one level up until you are at high priority. If you click again it goes back to low priority and so on.
Click twice on the blue dots for the "Meeting with George" task to set it to medium priority. You will see the blue dots change in color, but no other immediate changes. This only happens if you reload the list. Click on "Inbox" again and the list is reloaded with the new sorting.
As an alternative you can set item priorities with the context menu (CTRL-click your task) or with the Task Inspector.
Although our "Meeting with George" is important, our "Meeting with CEO" is even more important. You can flag a Task to mark especially important Tasks.
Click the gray flag on the right side of the task to flag it (1). The flag changes to red. If you click it again it gets unflagged. You will again only see the flag appear/disappear, but no other changes. Only after reloading the list the flagged items will be sorted at the top (with the default sort order).
As an alternative you can change task flagging with the context menu (CTRL-click your task) or with the Task Inspector.