Note:
If you are working in synchronous mode, you must have one or more sketch elements available to use as your cutting plane shape before you can select the Section command. See Defining 3D sections of models: best practices.
Choose the PMI tab→Model Views group→Section command 
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(Optional) On the Section command bar, click the Options button.
In the Section Options dialog box, edit or confirm the default settings for section caption, dimension style, and cutting plane annotation.
(Select Sketch Step) In the graphics window, click one or more sketch elements to specify the cutting plane shape, and then click the Accept button on the command bar.
(Side Step) In the graphics window, click to identify the side of the model you want to remove material from.
(Extent Step) On the command bar, click the Finite Extent option, and then define the thickness of the material you want to remove.
Example:
You can define extent graphically and enter a value in the Step box to control cursor movement. Or you can type a specific value for the extent in the Distance box.
(Select Parts Step) On the command bar, from the Cut List, choose whether you want to cut all the parts in the model, cut only the selected parts, or cut only the unselected parts.
If you choose Cut Only Selected Parts, then in the graphics window click the parts you want to cut away, and then click Accept.
Click Preview to see a graphical preview of the section.
Click Finish to create the section view. Look for the section name in the Section Views collection on PathFinder.
Tip:
3D section views are associative to the models affected by the cut. When a model changes, the section view updates.
To specify how cuts are displayed, you can change the settings in the Section Display Options dialog box Section Display Options dialog box.