Snapping gives you additional control when creating, moving, rotating, and scaling objects by causing the cursor to “jump” to specific portions of existing geometry and other scene elements during creation and transformation of objects or sub-objects. The controls in this dialog set the snap strength and other characteristics such as the snap target.
You can specify the portion of the geometry where you will snap. For example, when Vertex is the active snap type, creating and transforming objects snaps to the vertices of existing geometry. You can specify any combination of active snap types to provide multiple snapping points. For example, if Vertex and Midpoint are active, snapping occurs at both vertices and edge midpoints.
The default snap type is Grid Points.
Snapping works at sub-object levels. For example, you can use snaps to position a gizmo to the object on which you're working, or snap it to other objects in the scene.
You must activate a viewport in order to use snaps. Also, the Z-axis constraints don't apply to the home grid or grid objects, since grids don't have a Z axis.
Settings are stored in the 3dsmax.ini file. The state of the snap settings persists from session to session.
Snaps take precedence over axis constraints. If you activate an axis constraint, such as Restrict to X, you can move the object only in X. But if you then turn on snaps, Restrict to X is suspended and not used.
You can override this by turning on Snaps Use Axis Constraint Toggle on the Axis Constraints toolbar, or by turning on Use Axis Constraints in Snap Options.
The most common Snaps settings are available from an optional toolbar. To toggle display of the Snaps toolbar, right-click an empty area of the main toolbar, such as the section under the Reference Coordinate System drop-down, and choose Snaps. The toolbar buttons are shown next to the relevant commands, below and in the Snap Options.
The same settings are also available from the snap quad menu, available with Shift+right-click.
To set grid and snap settings:
(3D Snap Toggle).
Grids And Snaps Grid And Snap Settings to display the Grid and Snap Settings dialog.
Snap markers appear when the mouse cursor is over existing geometry or on a grid, depending on the active snap types. Each snap type has a different display; clicking when the snap-specific display is visible snaps to that spot.
To display the Snaps shortcut menu:
To use both constraint and snaps, do one of the following:
Options tab Translation group, turn on Use Axis Constraints.
Transform Constraints from the Snap quadrant.
Example: To use 3D snaps and rotation transformations together:
Select the box and turn on 
(Selection Lock Toggle).
(3D Snaps Toggle), then click 
(Select And Rotate).
( Use Transform Coordinate Center ).
A blue icon displays when the cursor passes over a grid point.
To turn snaps on and off during an operation:
Use these check boxes on the Snaps tab to turn on any combination of snap settings.
After setting snaps, close the dialog using the Close button in the dialog's upper-right corner. Do not click the Clear All button, or you'll turn off all the snaps.
This label changes to display the temporary snap type used by the Override system. For more information, see Snap Override.
These are the standard snap types used for grids, mesh, and shape objects. Non-grid snap types, when active, take priority over Grid Points and Grid Lines snaps: if the mouse is equally near a grid point and some other snap type, it will choose the other snap type.
These options snap to objects or sub-objects in a NURBS model.
The NURBS snaps settings are aids for creating and transforming objects, and are not constraints. 3ds Max does not maintain the relationship between the NURBS object and other objects you create or transform.
Snaps to a CV sub-object in a NURBS curve or NURBS surface.
Snaps to a point sub-object in a NURBS model.
Grid Points
Endpoint
Edge/Segment
Midpoint
Face