how can i install safari?

It may not be gone at all.

If the Safari icon has disappeared from the Dock, just look for it in /Applications folder and drag it back to the Dock.

Or use Spotlight [magnifying glass] icon to search for it.

Safari is installed as part of the system software. If you somehow uninstalled it, you will need to reinstall macOS according to the instructions in the "Related Article" at the top of the page.