How to search for and display data from a MYSQL database.

I am being encouraged to add a search facility to my php/MYSQL based website that I built some years ago with the help of DWMX2004 and occasional help from this forum.

You can see it here. It provides people in Torbay, UK with information about local resources applicable to Mental Health issues.

As you can see the information on the site is currently displayed through choosing a pre-selected list of topics under a heading such as "Depression", or by selecting a particular service form a list. eg. "Citizens Advice Bureau".

All the relevant data is stored in a MYSQL database.

Could some kind person please point me to an idiot's guide which will explain in detail how I can add a facility to search the database for a particular word, input by the website user?