General Magento Support - How to Install a Magento 1 Extension
How to Install a Magento 1 Extension
This video explains how to install a Magento 1 extension.
It uses CM Marketplace as an example. The installation process for Magento 1 is the same for all extensions - the only thing that changes is the file name.
For more specific instructions, please check the installation guide of each extension. Head to the Magento guides.