Roblox 2008 Hud Shaders is a shader pack, not a regular resource pack. It draws a 2008-style Roblox client head-up display on your screen through visual effects, while the world keeps its normal blocky look. You need a shader loader such as Iris or OptiFine to run it.
Put the pack where the game can find it
1. Launch Minecraft with your shader loader installed.
2. Open Options > Video Settings > Shader Packs.
3. Click the button that opens the shader pack folder. This opens your shaderpacks folder, which is separate from resourcepacks.
4. Place the pack file in that folder. If it is a zip, leave it zipped.
5. Return to the game. The pack should now appear in the shader list.
Activate it
1. Click Roblox 2008 Hud Shaders in the list to select it.
2. Click Apply or Done. The screen may freeze briefly while the shaders compile.
3. Load a world or join a server.
The retro 2008 HUD should now sit over your view. Blocks, mobs and terrain should look close to vanilla, so your builds stay easy to recognize.
To turn the effect off, return to Shader Packs and choose the off option (Iris and OptiFine both have one). Your world is never changed, because the pack only affects what is drawn on your screen.