How to lock wifi so no one can use it?

You secure the network with a password and don't give anyone else the password...

If that's not what you're talking about, you're going to have to go into a bit more detail about what you're trying to accomplish.

That would be done on your WiFi router. Check the documentation.

angelinasobe wrote:

I don't have a router. Its wireless.

Yes. You do. That's where the wireless comes from...

If it's someone else's network, then they would have to secure it.

Start here and do not repost until these concepts are clear to you.

Without a basic understanding of these concepts any suggestion from anyone on this forum on how to do this would not make any sense to you and futher complicate your request.

https://en.wikipedia.org/wiki/Wi-Fi

https://en.wikipedia.org/wiki/Wireless_router

https://en.wikipedia.org/wiki/Wireless_security

https://en.wikipedia.org/wiki/MAC_filtering

Otherwise a local IT specialist or possibly someone in your neighborhood can likey assist you.

As per this article Recommended settings for Wi-Fi routers and access points - Apple Support

Security

The security setting controls the type of authentication and encryption used by your Wi-Fi router, which allows you to control access to the network and specify the level of privacy for data you send over the air.

Set to: WPA2 Personal (AES)

WPA2 Personal (AES) is currently the strongest form of security offered by Wi-Fi products, and is recommended for all uses. When enabling WPA2, be sure to select a strong password that can't be guessed by third parties.

If you have older Wi-Fi devices that don't support WPA2 Personal (AES), a good second choice is WPA/WPA2 Mode, also known as WPA Mixed Mode. This mode allows newer devices to use the stronger WPA2 AES encryption, while still allowing older devices to connect with older WPA TKIP-level encryption. If your Wi-Fi router doesn't support WPA/WPA2 Mode, WPA Personal (TKIP) mode is the next best choice.

For compatibility, reliability, performance, and security reasons, WEP is not recommended. WEP is insecure and functionally obsolete. If you must choose between WEP and TKIP, choose TKIP.

Due to serious security weaknesses, the WEP and WPA TKIP encryption methods are deprecated and strongly discouraged. Use these modes only if necessary to support legacy Wi-Fi devices that don't support WPA2 AES and can't be upgraded to support WPA2 AES. Devices using these deprecated encryption methods can't take full advantage of 802.11n performance and other features. As a result, the Wi-Fi Alliance has directed the Wi-Fi industry to phase out WEP and WPA TKIP.

If your security is set to None or unsecured mode, you're using no authentication or encryption. Anyone can join your Wi-Fi network, use your Internet connection, access any shared resource on your network, and read any traffic you send over the network. Using an unsecured network is not recommended.

Open system preferences - network open the pad lock by entering admin name and password ( if it is an admin account ) , click on advanced - select wifi - under network preferences , click on plus sign a window appears , fill up the credentials

make sure location is set to automatic , correct DNS server settings are added , no proxies should be added , join this network automatically box must be checked , come to first window and click on apply .