HUD

The HUD (heads-up display), or UI (user interface), has many different bars and options.

At the bottom left, there are seven bars in total. The five along the left, in descending order are: Along the top is the temperature bar, which moves from either left or right if you get colder or warmer. The bar along the bottom is the experience bar.
 * energy (yellow)
 * health (red)
 * hunger (orange/brown)
 * thirst (blue)
 * weight (purple).

In addition to this, there are weapon and item slots. Ten of them are visible in between the experience and temperature bars. Along the right there are also six additional, smaller slots that may be used for other things.

Along the left is a chat box, which also has buttons that open various things along the top, like the settings.

This screenshot was posted by the developers on the Rend Discord.