If you have beat Spider-Man for the PS4, but still want to play more, then New Game Plus is for you. This game mode allows you to begin the game from the start again, but you get to keep all your suits, skills, gadgets, benchmark, mods, and all other unlocks. All the open world activities reset tough, and you are able to begin the game again with a harder difficulty.
As mentioned above, you need to complete the main game before you can begin a New Game Plus in Spider-Man. This is done with you have put all the enemies behind bars and beaten the final boss of the game. You'll know that you have completed the game when you see credits rolling.
It's entirely possible to keep playing the game after having beaten the main story line, but if you want to make a New Game Plus, go to the main menu and locate your save file. Instead of just loading this like usual, press Square to create a new save file with the New Game Plus mode.
After this just select your New Game Plus save file to begin the NG+ adventure!