To cut potatoes into fries, follow these simple steps:

1. Start with a long potato (such as russet) for best results.
2. Using a sharp chef's knife, slice the potato in half lengthwise.
3. Lay each half flat-side down on the cutting surface.
4. Slice the potato lengthwise into 1/4 to 1/2-inch thick slices, depending on how thick you want your fries.
5. Stack a few slices and then cut them lengthwise again to create evenly sized fries.
6. Optionally, soak the cut fries in cold water to remove excess starch, which helps make them crisper when cooked.
7. Drain and dry the fries thoroughly before frying or baking.

This method gives you uniform fries that cook evenly and can be adjusted for thickness preference. If you want crispy fries, thinner cuts work best, but be sure to handle them gently to avoid breaking.