The Crossing Restriction Panel (CRP) is designed to provide a direct way of achieving a 4-D trajectory (x, y, z, time).  Indirectly, it gives you added control over an aircraft's vertical path, or pitch.  Consistent with the other Flight Deck Controls, the fields in the CRP use the same color scheme.

Clicking on "Cross" displays a drop-down menu of the different fixes available for your aircraft to cross at.  Think of the available fixes as "possible fixes," meaning if an aircraft has gone past a fix, that fix will be gone from this list of available crossing fixes.  You can use your keyboard to directly type in this field, if a desired fix is not in the list.

Clicking on "Alt" displays probable altitudes to cross the fix at.  You can also click the actual altitude field and type in an altitude if it is not in the drop-down menu.

Clicking on "Spd" shows a drop-down menu of the common speeds assigned in crossing restrictions.  Similar to altitude, you can also click the actual speed field and type in a speed if it is not in the list.

In this example, TWA263 is approaching the waypoint MOOSE.  According to the CRP, the fix field is engaged, implying the aircraft will cross this fix.

The other fields are in yellow, meaning these values are the predicted results if the aircraft is left alone.

Note that what is in the CRP is also displayed on the Map display (with route information turned on). 

Here all three fields are engaged, and their values are also reflected in the Map display (with route information turned on).

The CRP values affect your aircraft's vertical path.  Notice that under the new crossing restriction, the VNAV TOD (Vertical Navigation, Top of Descent) is now behind TWA263.  This corresponds to the PFD displaying VNAV PTH.