Question for Beginners: how to use regular expressions in PHP

Q: How do I use regular expressions in PHP? Preg_replace ('(& lt; img) (. *) src = (\ S *) & gt ;? ', & Quot; $1 $ 2src ='/images/po.png 'lazy-src = $3 & quot;, $ data); regular expressions are only used by new users in development tools: how do I use regular expressions in PHP?
Preg_replace ('(? ', "$1 $ 2src ='/images/po.png 'lazy-src = $3", $ data );

Regular expressions are only tested correctly in development tools, but cannot take effect in PHP. Is it correct to use them?

PHP is not proficient. please advise.

------ Solution --------------------
Echo preg_replace ('/(? /', "$1 $ 2src ='/images/po.png 'lazy-src = $3", $ data );