This is the third query you have posted about access to plugins and the answers to those will answer this one two.
If you have a specific problem with a plugin, name the plugin you are trying to use and what you have done in your attempts to use it, install it or download it.
Read the previous answers as in my first sentence above.
Put the plugin in the /plugins folder and then use the back office to install it as indicated before.
General Support
This is the third query you have posted about access to plugins and the answers to those will answer this one two.
If you have a specific problem with a plugin, name the plugin you are trying to use and what you have done in your attempts to use it, install it or download it.