InDesign defaults to picas as the unit of measurement. You can change that to inches by going to the Edit menu, then Preferences, and then choose Units & Increments (on the Mac go to the InDesign menu, choose Preferences, and then Units & Increments to change to another unit). In the Ruler Units section, change the Horizontal and Vertical pulldown menus to your preference.
If you are using InDesign for a poster, be sure to put in the desired print dimensions.
To start a new document, go to the File menu, choose New, and then select Document… In the New Document dialog box,
Sometimes you need to adjust the document’s settings, after you've created it.
Select/deselect Facing Pages: go to the File menu and select Document Setup….
Adjust the margins and columns: go to the Layout menu and select Margins and Columns…. When adjusting the margins, pay attention to whether the linked icon is selected. If it is linked, making a change for one of the margins will make the others change as well; if it is not linked, each margin will remain independent of each other.
View this Tutorial on this new CS6 layout feature: