Just write whatever information you feel is necessary to a file, and include in the program the logic to read that file and restart the player from a specific point in the game rather than at the beginning.
Tip: Write it out in text format first, then it's easy to read and to edit. Binary files can be a pain but once you've got it sorted you can switch to a binary format if you like.
Tip 2: sort out the file read logic first, using hand-crafted savegame files. Once you know what you need in the file you can then write the file write logic.