After uploading the addons to your server, you need to activate the desired addons in the Admin panel. Addons not activated have no effect on your node.
Among these addons there are also the [connectors](https://github.com/friendica/friendica/blob/stable/doc/Connectors.md) for various other networks (e.g. Twitter, pump.io, Google+) that are needed for communication when the protocol is not supported by Friendica core (DFRN, OStatus and Diaspora).
For communication with contacts in networks supporting those (e.g. GNU social, Diaspora and red#matrix) you just need to access the page configuration in the Admin panel and enable them. For networks where communication is only possible the API access to a remote account, you need to activate the fitting connectors.
The addon interface of Friendica is very flexible and powerful, so if you are missing functionality, your chances are high it may be added with an addon.
Read more about the workflow in the [Friendica translation documentation](https://github.com/friendica/friendica/blob/stable/doc/translations.md#addon).