On many newer MacBooks if you have an internet connection you can reinstall your MacOS. All you have to do is turn on your MacBook, and hold down the option, and the R key, and it will boot to recovery mode if your MacBook supports internet recovery.
If you have an ethernet network available and you can plug your MacBook into the network cable, it will go much faster than if you use wireless.
If you don't have ethernet, your MacBook will have you join a wireless network, and you can proceed.
There is more than one way to install a MacOS, and you should familiarize yourself with some of the different options, and hard drive partition choices.
Below is a couple videos that may be helpful. Make sure you have all of your data backed up, and you have verified you can access your backup before you begin. In many of the options, you will be destroying all of your MacBooks's data, and you need to be sure you have it securely backed up.