GUI message scripting need help to create a info box

I am making a post apocalyptic mmorps and I want to make a gui message on screen so that when my player is at lets say 10% health A message pops up saying: You are almost dead please go hide! Or when the condition of his weapon breaks: Ur weapon is broken if you keep using it, it will become unusable! Also ones that say when hes entered a new area, completed a mission, his current mission,etc.

It needs to fade in kinda naturally so that it doesn't look super bad. Also Id like to apply my own texture to it so that it would look how I wanted it.

If someone could point me to a tutorial to show me how to do this or TEACH me how to do it I would greatly appreciate it.

Always Newb,

Tracey