How to Install and Activate the Pixels Simple Hud Resource Pack
Placing the Pack in the Right Folder
A resource pack only changes how your game looks, so it must sit in the correct folder before Minecraft will list it. Open your game's resource pack directory from the in-game options menu, or navigate to it manually through your launcher's folder shortcut. Drop the Pixels Simple Hud pack file (or its unzipped folder) directly into that directory. Do not nest it inside another folder, or the game will not detect it.
Enabling It In-Game
Launch Minecraft and go to Options, then Resource Packs. Find Pixels Simple Hud in the left-hand column of available packs and click the arrow to move it to the selected column on the right. Click Done. The HUD should refresh immediately — you will see the new hearts, hunger icons, and armor points above your hotbar.
Checking It Worked
Enter any world and look at your health and hunger bars. If the icons still look vanilla, the pack is either not selected or placed in the wrong folder. Make sure no other HUD pack sits above it in the selected list, since the topmost pack wins for any overlapping textures. If you play Hardcore, start a Hardcore world to confirm the alternate heart style appears.