Drag the .zip file into the folder. Do not unzip it. The pack should appear in the left column. Click the arrow to move it to the right column (Active).
For the best experience on Eaglercraft, use these widely trusted 1.8.8-compatible packs: Xray Ultimate 1.8
Provide instructions on Explain how server Anti-Xray technologies work
Installing a resource pack in Eaglercraft differs slightly from standard Minecraft because it runs in a browser environment. Follow these steps to upload your pack: 1. Download the Texture Pack