When I connect to my WiFi network it’s showing privacy warning what does it mean and how to get my network secured

Apple is referring you to their Recommended settings for Wi-Fi routers and access points. Your iPhone has detected a security setting on the network which is lower than Apple's recommendation. It is not saying that your network is insecure. Security settings have moved on to a higher standard than a few years ago, and the recommended setting are described in the linked document. Apple recommends:

• WPA3 Personal is the newest, most secure protocol currently available for Wi-Fi devices. It works with all devices that support Wi-Fi 6 (802.11ax), and some older devices. 
• WPA2/WPA3 Transitional is a mixed mode that uses WPA3 Personal with devices that support that protocol, while allowing older devices to use WPA2 Personal (AES) instead.
• WPA2 Personal (AES) is appropriate when you can't use one of the more secure modes. In that case, also choose AES as the encryption or cipher type, if available.

Older standards which are no longer recommended are:

• WPA/WPA2 mixed modes
• WPA Personal
• WEP, including WEP Open, WEP Shared, WEP Transitional Security Network, or Dynamic WEP (WEP with 802.1X)
• TKIP, including any security setting with TKIP in the name

But as most people use hardware either until it dies, or until they want a faster speed the older settings will be found on many home networks for some time to come. Only recent routers, including those with Wi-Fi 6 (otherwise known as 802.11ax), compliy with WPS3.