Do any of the following:
Show or hide the sidebar: Choose View > Show Sidebar or View > Hide Sidebar.
Resize the sidebar: Move the pointer over the right edge of the sidebar until the pointer changes, then drag to make the sidebar wider or narrower.
Rearrange reminder lists in the sidebar: Drag the reminder lists in the sidebar into the order you want them.
Show or hide standard Smart Lists: Choose View > Show Smart List, then select or deselect a Smart List.
Pin a reminder list: Control-click the name of a reminder list, then choose Pin List. After you pin a list, it moves to the top section of the sidebar. To move the pinned list back down to the lower section of the sidebar, Control-click the list, then choose Unpin List.
Note: You can have a total of up to nine pinned lists and standard Smart Lists.
View the reminders in a list: Select the list in the sidebar.
View a reminder list in a separate window: Double-click the list in the sidebar.
View multiple reminder lists: Click the All Smart List, or click a list group’s title to show all the lists in that group
Go to the Reminders app Mark reminders as completed or incomplete on Mac