Use the Relationship Assistant command to automatically place dimensions and relationships on existing profile or sketch elements. Use the Sketching tab→IntelliSketch command to place dimensions and relationships on any new 2D elements as you draw them.
In 3D environments, highlight and lock a sketch plane.
To learn how, see the Help topic, Lock or unlock a sketch plane.
Choose Home tab→Relate group→Relationship Assistant 
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On the Relationship Assistant command bar, click Options.
In the Relationship Assistant dialog box, specify which types of geometric relationships and dimensions you want to add.
In the graphics window, select the elements you want to add relationships or dimensions to and then click the Accept (check mark) button on the command bar.
If you set the Horizontal Locations option on the Relationships Assistant dialog box, click the element you want to use as the origin for horizontal dimensions.
If you set the Vertical Locations option on the Relationships Assistant dialog box, click the element you want to use as the origin for vertical dimensions.
Tip:
The element you select as the origin for horizontal dimensions is typically perpendicular to the horizontal dimensions, such as a vertical line that is vertical in the view.
The element you select as the origin for vertical dimensions is typically perpendicular to the vertical dimensions, such as a horizontal line in the view.