How do I create a HUD?

I haven't played around with HUD's much, but I believe you create an "Overlay" mod element. :) Hope you can figure the rest out, because that's all I know XD

Use overlay condition builder.

That isn't so easy to do. You can only do that through coding. Pretty advanced coding as well I believe.

Fun fact - if you go into the text based editor and look at the general structure of it and create more then one overlay with small changes, you can look for the changes and compare them to a blank "control sample" overlay that has nothing in it,
to understand how things are added to the overlay in the code itself ;)

Its hard but once you kinda understand the general structure, you can learn off it!
and use it to insert values into areas they should not be ;)

like for instance, inserting an item id slot value from the player entity via a gui's bit of code, into a text display of an overlay, to display a really strange item id value as text!

lol!

You will have a lot of fun with this, who knows,
pehaps you will figure out how to make a health bar display with images via looking at the code of other mods!
 

the java format is the same with other mods!!!

use 7 Zip or something to view the contents of a jar file of a random non Mcreator mod

and look for some kind of HUD - Overlay - GUI
that has a health bar in it!
 

then just copy and paste, learn off, edit and add stuff to your code via the code of that mod's files ;)

its really cool and i really recommend messing around with it.

for instance, 

i made a modeled 3D eatable food item of a tomato that has an ore table for other mod support and all!

but its eating effects are missing textures lmao...

but it still works :P