If I delete a game, will it also delete my saves?
To answer the title question, no. You can delete a game from the HDD without it deleting your save game data and files.
To answer the body question - under settings, you go to where you manage storage (navigation is self-explanatory and easy to figure out if you're a first time user). You'll be able to delete game data AND save data, indicating these are two separate files. Delete only the game data and if you decide to reload the game later, you will pick up right where you left off.
I've done this countless times.