Here you can watch vieoguide about installing modules in PrestaShop 1.6. Video is recorded for customer purposes that asked about detailed instructions. I think that this explanation will meet all requirements. Step by step guide about installing custom .zip module library in shop based on 1.6.x engine.

Text instructions

1. Log in to shop back office
2. Go to "modules > modules" section
3. Click on "add new module" (field to upload custom file will be visible then)
4. Select downloaded .zip module file
5. Click on "save"
6. After that click on green "install" button
7. page will refresh now
8. If module has got configuration page - you will be redirected to that page
9. If module doesnt have own configuration page - page will refresh only