html – Call one more php without leaving the defaults

I am a newbie in internet programs and also currently I am stuck, so I want to request your aid.

As you can see, the food selection gets on the left and also alongside it the “web content” area or something like that where i want to see tables, and so on. What are called by the food selections when i click it. Just how can I call one more php code like u can see listed below? For instance, if you click the clients, it draws out the clients in a table in the “web content” area alongside the food selection without leaving the web page and also whatever exists simply there is currently the clients and also not the setups or something like that.

My index web page Code:

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