Actions - Most actions require the use of at least one hit point. Additional hit points might be used to maneuver, manipulate an opponent, cause damage or recover from damage. (See Action Rules/Hit Points/Recovery, Action Rules/Maneuvering, Action Rules/Manipulation, and Action Rules/Attacking.)
Readying weapons - Unless surprised, characters will usually draw their weapons before the beginning of combat. If they have to ready the weapon during an action round, drawing the weapon from it's sheath, holster, scabbard, belt, or other convenient location usually requires the use of one hit point.
Parrying - A character may use a one hit point action to defend (interfere with an attack) with an item. This lets the character use the item's special parry bonus to improve their bonus to defend against the attack. (See Equipment/Armor and Weapons/Parry.)
Loading weapons - Some weapons must be loaded before each atack, or reloaded after a certain number of uses. If the ammunition is in a convenient location (a quiver, pocket, pouch, bandolier, etc.) it can be drawn from that location with an action that uses one hit point. Then the ammunition can be loaded into a simple weapon like a sling or a bow with another action that uses one hit point. More complex weapons may have extra steps that use more hit points. If you have to load a revolver one bullet at a time for example, you must use an extra one hit point action to load each bullet.
Unloading weapons - Most weapons are designed to be loaded quickly, but unloading them can be trickier. Unloading a weapon is usually a one hit point action, but then you are either holding the ammunition or let it drop (your choice.) Putting away the ammunition you are holding requires an extra one hit point action - assuming that you have a single convenient place to put it. (If you have to load several rounds of ammunition into individual locations, each round of ammunition will take a seperate one hit point action.)