How would i add a progress bar and an energy meter in a custom furnace?

i still dont know for progress bar, but for energy meter, just add a text label on the GUI, and where u put the text, there is an arrow, at the right of the text input, just click on it, and scroll down till u see <energy> and click on it. after u can do this: <energy>/(Max amount of energy)

You can create it using images and display conditions. I can explain in more detail if you want