On the file selector dialog Files Of Type drop-down list, choose "Alembic (*.ABC)".
Choose an ABC file to import, then click Open.
On the import options dialog, set the two options as appropriate, then click OK.
Import to Scene Root
When on, objects in the ABC file are imported to the root level of the scene, as "children of the world." When off, objects in the ABC file are imported as children of a Dummy object named Alembic. Default=off.
[animation options]
Fit Time Range (The default.) When chosen, changes the active time range to match the animation in the ABC file.
If the ABC file is not an animation, the active time range does not change.
Import and Start at Current Frame When chosen, does not change the time range of the current scene. Animation from the ABC file begins at the current frame. If the ABC animation is longer than the current time range, the animation is truncated.