The difference in potatoes really comes down to how starchy or waxy they are—which is, in turn, related to the potato’s moisture content.
What we normally call a baking potato—or a Russet or Idaho—is a high starch potato. It is low in moisture and makes great, fluffy baked potatoes and is ideal for French fries.
For more information on baking potatoes, see 7 Ways with Baking Potatoes.
Boiling potatoes—a.k.a. red potatoes or red bliss, are waxy. They are lower in starch, which means when you cook them, they retain their shape better. Use boiling potatoes for potato salad. As an added bonus, the thin red skins also look nice in a salad—and leaving them on packs in extra nutrients.