There are four main Operations in the game: Travel, Eat, Sleep, and Work. They are technically not systems in and of themselves, but are a logical abstraction connecting related Events to respective Mechanics.
Every Operation is triggered by interacting with objects in the current Location. Most Operations are nested within a singular object - for example, interacting with a job board might present multiple potential Work Operations. In turn, each Operation is associated with a single Event - and if that Event has any specific requirements, such as only being available during specific Time Segments or requiring the player to have an amount of Money to spend in exchange for the Event, then those requirements are presented to the player when considering the Operation.
It is important to note that not all Locations will have options for all Operations - some strategizing and planning ahead would be in the player's best interests, especially as they progress later in the game. Playing by the seat of one's pants may be all fun and games until a Travel Operation takes you to a Location that doesn't have any Eat Operations available, and you don't have any Food Stores in reserve.
Travel is a unique Operation, in that it is always available regardless of Location, and there are three specific subtypes of Travel - any Travel Event must be specially marked as to which subtype it belongs to, which is a requirement unique to Travel Operations.
This is because, unlike Eat, Sleep, and Work operations, Travel operations do not take place within Locations, but instead exist between Locations.
The three specific subtypes of Travel are as follows: