Website Global Message [on hold]

I'm wanting to add a global message to my website. What I mean is I want a message that will appear on every page whenever I change it. I am coding the website myself and just need some help with this. I have very little experiment in PHP and Js (only really know HTML and CSS). If it is possible could you please direct me to a tutorial or just write a little step by step instructions.

What's Needed? -A global way of displaying messages over different Pages on my site -I know no Js or PHP, so please be descriptive (Thanks a lot for the help) -I am also using the BootStrap framework if that makes a difference

Thanks So Much It Means A lot Kind Regards