How can i get a working point system? (zombies)

Hello fellow developers,

i’d like to ask for some help! Me and my friends at school got a project on making a game, we chose zombie survival (fan made black ops zombies) but we want to have requierd points to open doors and we want to be able to get points by killing the zombies, however i could not find any tutorials on how to do this.

Please help us!

Thanks in advance!