Latisse comes as a drop, with a supply of applicator brushes. One package is about a month's supply, with 60 brushes. Although not recommended by the manufacturer, you can choose to use one brush for both eyes, which might give you more than a month per box.
To use Latisse, you apply a drop to the brush, then gently brush the upper eyelid at the base of the lashes. The lower lid is not treated.