A majority of whole turkeys sold under "major brands" in the US now have a "preinstalled thermometer" with a little "pop up" button that indicates when the turkey (near the button) reaches the recommended 185F (85C) temperature. This is generally a safe enough indicator, especially for an "unstuffed" bird. Stuffing may slightly affect the temperature distribution within the whole, so that you might also want to sample temperatures in a few places within the whole pan if there's any question.

The most convenient meat thermometers generally have a fairly small diameter metal tube extended from the indicator with a point on the end so that you can punch it into the meat. Closely similar thermometers with a blunt or "squared off" end are more suited for checking temperatures in a pot of liquid goo.

In use, the tip of the meat thermometer should be "in the meat." A fairly common error is pushing the thermometer in too far so that it's actually sensing the air inside the turkey cavity.

Although it's unusual to find a decent quality meat thermometer that's far out of calibrations, it is a good idea to do a spot check if there's any question. The "needle" is connected to the sensor, in a small space at the end of the tube, and nearly all such thermometers have a "nut" of some sort that allows you to turn the dial to line up the "what it should say" with where the needle points. For meat, sticking the end of the thermometer in some water (at a full boil) should provide a sufficiently accurate 100C/212F reference temperature for aligning the dial with the needle. (It may not be obvious that your meat thermometer is "adjustable," but nearly all of them actually are.)

While we often put some stuffing in (and around) the birds, our only purpose there is to absorb some of the grease that cooks out of the meat to keep the meat on the bottom from getting slimy, and we generally discard that stuffing and eat what we bake separately in a separate "cake" pan. There are also lots of recipes you can use to cook stuffing in a pot (e.g. the widely advertised "Stove Top Stuffing," although we prefer other recipes) that's much quicker and provides a simple method that gives consistent results. It's also easier to fix small batches of "stove top" recipes, so that you can have a couple of varieties instead of one-size-for-all if you like.

I've tried saving the old bread ends & such for stuffing, but "someone" in the house invariably gets into "get the place cleaned up for the party" mode and tosses them all the day before it's time to start cooking, so we usually end up with "fresh stuff" despite it's somewhat "commercial flavor."

John