If you look at the item description for most Crossbow-type weapons, they usually have a property called Loading, which is described like this in the Player's Handbook:
Loading. Because of the time required to load this weapon, you can fire only one piece of ammunition from it when you use an action, bonus action, or reaction to fire it, regardless of the number of attacks you can normally make.
The consequence of this is that the time and effort required to load a crossbow—the action you're looking for clarification on—is normally abstracted as simply being part of the process of firing the weapon, the consequence being that it prevents using the crossbow more than once per attack-action.
The Crossbow Expert feat eliminates the time needed to load a crossbow
Among its other features, the Crossbow Expert feat permits a user to gain the normal benefits of their Extra Attacks feature when using a Crossbow:
Thanks to extensive practice with the crossbow, you gain the following benefits:
- You ignore the loading quality of crossbows with which you are proficient.
- Being within 5 feet of a hostile creature doesn't impose disadvantage on your ranged attack rolls.
- When you use the Attack action and attack with a one-handed weapon, you can use a bonus action to attack with a hand crossbow you are holding.
So if you take this feat, you can ignore the cost of loading a crossbow altogether.