Hello why when i trie to connect wifi on xbox 360 it says to use a wireless internent...

A modem is the device that allows your devices to connect to the internet. You'd only be able to have one device connected at any one time unless you have a router connected in your setup as well. It would be best to contact your ISP if you have any questions regarding this.

Are you trying to connect your Xbox 360 on a wired connection with an Ethernet cable? Are you trying to create an account or sign in to an existing one, and what's the specific error code/message you receive?

Hi Jaden, I’m Ryan.

What Xbox 360 model do you have? All the ones prior to the Xbox 360 S required the network adapter (as the consoles didn’t have built-in WiFi) for an internet connection to Xbox Live.

Refer to his support article for the steps:
https://support.xbox.com/help/xbox-360/accessories/how-to-connect-xbox-360-wireless-network-adapter

Troubleshoot your Xbox 360 network connection:
https://support.xbox.com/help/hardware-network/connect-network/xbox-360-network-connection

Here to help.

Hello i wannt to ask what is a modem when i tried with internet cable when i trie to open xbox360 live account at the end it dont work it says error code and something

It can be a wireless issue, can you trie to use a cable connection?

Im pretty sure that you cant use the old wifi adaptors with the xbox 360 slim because the internal wifi connection utilizes wifi-N, the newer standard of wireless connections and may not properly interface with the xbox 360 slim.

As for getting a better signal.... i dont think it really makes a difference, most issues regarding that usually are environmental issues surrounding the 360 and nearby access point or the router. For instance having thick walls, microwaves, other computers
running wireless, etc.