Install the package the usual way.

You'll have a new item under Dashboard > System & Settings > Environment > Constants Driller:

The url of this page will be the following:
/dashboard/system/environment/constants_driller

The the top of the Constants Driller page looks like this:

In the first text field you can specify the constant name (or a sub-part of it).

In the drop-down menu you can specify if you're looking for a definition of a constant and/or for its usage.

In the last text field you can insert a path (or a sub-part of it): if specified, the resulting constants will be only those that are defined and/or used in files in that path.

The Exclude 3rd party libraries checkbox allows you to filter out the constants that are defined and used only inside the third party libraries of your concrete5 installation.