There are a lot of confusing wine terms. And there seems to be constant confusion over the difference between a variety and a varietal. Yet, it's quite simple.
Old World wines, most notably from western European countries such as France, Italy, Spain and Germany, identified their wines by region. So, with French wines, you'll find the wines of Bordeaux, Burgundy, the Loire Valley and the Rhône Valley. Italy has Chianti, Spain has Rioja and Germany has Pfalz and Franken. If you know the region, you know the wines and the grapes used to produce them.
But the New World, most notably California, decided on a different tact. Instead of just growing grapes by regions, the early winemaker found that California's climate and soils were excellent for growing many grapes and producing many wines. So, they focused on selling wines that identified the type of grape used in its production. This is where the two words come in. Various grape varieties are used to produce varietal wines. While Chardonnay, Cabernet Sauvignon and Pinot Noir are each a grape variety, when they are used exclusively to produce a wine, the wine is considered a varietal wine.
Now, as usual, things are never quite so simple. In California, wines using varietal names must derive at least 75% of their volume from the grape variety designated. So, yes, when you buy a bottle of Cabernet Sauvignon, it's made from the Cabernet Sauvignon variety of grape. At least 75% Cabernet Sauvignon grapes. The other 25% of the grape variety(s) used can be left to the winemaker's creativity.
Nonetheless, just remember when you pick up a bottle of Cabernet Sauvignon, know that you are purchasing a varietal wine made with the Cabernet Sauvignon variety of grape. Cheers!