Freestyle dining (there is more to freestyle then just dining) can be confusing but in fact is very simple. Since you are considering the Gem I will describe it on that ship.
First foget all the alternative dining options The Gem like most ships has two main dining rooms like most ships. The difference to set seating times or table. Show up when you want between 5:30 and 10:00 pm with who ever you want. Table for 2 or a table to dine with the new friends you made onboard. You can even request to be seated with others that want
to sit with others. Unlike anytime on Princess you will never be asked to sit with others unless you ask. If you want you can make a standing reservation in the main dining room at the same time but normally that is before 6:30 or after 8:30. As on land the busiest time is between 7 & 8.
You always have the option of the Garden Cafe Action Station Restaurant. This is not your normal ship buffet but rather a gathering of islands that prepare food just about to order or in small batches or carved to order
You also have the Blue Lagoon for hour "fast" food, poolside food options, and room service with a limited menu.
All of the above with no sercharge like any ship.
Now add to that the option to make reservations at a number of alternate dining venues. Reservation can be made the same day or up to hours in advance for all passengers, 8 hours in advance for Balcony and mini suite passengers, or for the whole cruise with the conceirge in a penthouse.
On the Gem you have an Itailian or Tex Mex for $10 both offer a lobster special. Ravioli and a lobster taco.
The Bistro at $15 is a french themed venue. Escargots to die for.
Cagney's steak house $20 with tbones,filet, rib eye, lamd & veal chops, sea bass, chicken.....for an extra $10 live lobster cooked to order or a giant porterhouse. Great shrimp cocktail and don't miss Cagney's fries made with white truffel oil
You have an Asian option with sushi bar $15
And finally for $25 the most fun dining at Tepaniaki
How much or little of Freestyle dining you take advantage of is up to you. Some folks eat in the Garden Cafe every day, others the main dining rooms like a traditional cruise, and then there are fpassengers like me that try to eat in every different venue on every cruise.