I'm confused about difference between a hotel manager and general manager. Who reports to who, with these two titles being so similar?

The General Manager is the person who oversees all hotel operations. The Rooms, Food and Beverage, and all back office functions (Accounting, Sales, Engineering) report ultimately to the General Manager.

Sometimes the title Manager is an abbreviation for Front Office Manager or Rooms Division Manager. This person is responsible for the Front Desk and Reservations and possibly Housekeeping. Manager can also be applied to a person responsible for the hotel while the General Manager is away. Usually, on weekends, a hotel Manager will oversee operations while the General Manager is off.

In larger hotels, Manager may be a permanent position - one step below the General Manager. In smaller hotels, the weekend Manager is a position that rotates by week among Department heads.

Sometimes I get the impression that "manager" means "manager on duty". In other words the chief manager in charge of the hotel at a particular moment (when the general manager may be off duty).

Sometimes there are also "Directors" such as a Food and Beverage Director and Rooms Director. At very large properties, you might also find a Director of Operations (typically #2 in the chain of command). The head of HR and Sales & Mktg can also be a Director.