Customize menu > Grid And Snap Settings > Grid And Snap Settings dialog > Snaps tab
Main toolbar > Right-click a snap button
Keyboard > Hold Shift+right-click > Snaps quadrant
Keyboard > S (toggles snaps on and off)
Snaps give you control when creating, moving, rotating, and scaling objects, because they let you snap to specific portions of existing geometry 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.
Note: Snap functionality includes several features that enhance ease of use. See the Snap Options topic for details.
You can specify the portion of the geometry where you will snap. For example, when Vertex is active, creation and transforms snap to the vertices of existing geometry. You can select any combination to provide multiple snap points. If Vertex and Midpoint are active, snaps occur both at vertices and at midpoints.
Grid Points is the default snap type.
Note: Snaps are not on by default. Turn snaps on and off with the S key in the middle of a transform. You can use snaps with free positioning this way.
Snaps work 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. (Prior to version 3, snap settings were stored in the maxstart.max file.)
Snaps take precedence over axis constraints. If you highlight 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.

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 topic.
The same settings are also available from the snap quad menu, available with Shift+right-click.
3ds Max offers two different types of snap behavior. You can use snaps to move a selection to a snap point, an absolute snap. You can also use snaps to move a selection a relative distance from a snap point. This is called a relative snap. For further information, see To use relative snaps:.
To set grid and snap settings:
Choose Customize > Grid And Snap Settings to display the Grid and Snap Settings dialog.
In the Snaps tab, select one or more of the types of snaps you want active.
Create an object or transform an object.
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.
Example: To use 3D snaps and rotation transformations together:
From the Use Center flyout on the main toolbar, choose Use Transform Coordinate Center.
Activate the Perspective viewport and move the cursor over the grid.
A blue icon displays when the cursor passes over a grid point.
When the blue icon displays, click and drag to rotate the box around the selected grid point.
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.
Override—This label changes to display the temporary snap type used by the Override system. For more information, see Snap Override.
Clear All—Turns off all of the Snaps check boxes.
Note: The layout of the Grid And Snap Settings dialog is generated at runtime. Because of this, it might appear slightly different than the illustrations shown here.

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.
Note: The button images shown below are from the Snaps toolbar.
Grid Points—Snaps to grid intersections. This snap type is on by default. Keyboard shortcut=Alt+F5.
Grid Lines—Snaps to any point on a grid line.
Pivot—Snaps to pivot points of objects. Keyboard shortcut=Alt+F6.
Bounding Box—Snaps to one of the eight corners of an object's bounding box.
Perpendicular—Snaps to the perpendicular point on a spline, relative to the previous point.
Tangent—Snaps to a tangent point on a spline, relative to the previous point.
Vertex—Snaps to vertices of mesh objects or objects that can be converted to editable meshes. Snaps to segments on splines. Keyboard
shortcut=Alt+F7.
Endpoint—Snaps to the end points of edges on meshes or spline vertices.
Edge/Segment—Snaps anywhere along edges (visible or invisible) or spline segments. Keyboard shortcut=Alt+F9.
Midpoint—Snaps to the middle of edges on meshes and spline segments. Keyboard shortcut=Alt+F8.
Face—Snaps anywhere on the surface of a face. Back faces are culled, so they have no effect. Keyboard shortcut=Alt+F10.

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. The software does not maintain the relationship between the NURBS object and other objects you create or transform.
CV—Snaps to a CV sub-object in a NURBS curve or NURBS surface.
Point—Snaps to a point sub-object in a NURBS model.
Curve Center—Snaps to the center of a NURBS curve.
The center of a NURBS curve is calculated parametrically, and might not be the same as the curve's apparent visual center.
Curve Normal—Snaps to a point normal to a NURBS curve.
This snap operates only while you are creating a new object that requires two or more clicks to create.
Curve Tangent—Snaps to a point tangent to a NURBS curve.
This snap operates only while you are creating a new object that requires two or more clicks to create.
Curve Edge—Snaps to the edge of a NURBS curve (the current object moves or is created to lie along the curve).
Curve End—Snaps to the end of a NURBS curve.
Surf Center—Snaps to the center of a NURBS surface.
The center of a NURBS curve is calculated parametrically, and might not be the same as the curve's apparent visual center.
Surf Normal—Snaps to a point on a NURBS surface normal to previous point.
This snap operates only while you are creating a new object.