This is a very short article introducing you to very useful package for your local computer or laptop: a File Transfer Protocol package, to install on your computer, or laptop.
This is not a Joomla!® specific package and can be used to download and upload files, folders, and packages between your local computer or laptop and your website server.
While there are various ways of downloading and uploading files between your computer or laptop and your hosting provider hosting account here at UsingJoomla.com we recommend: CuteFTP
CuteFTP can be used, as an example, to download your Joomla!® backup archives, upload your backup archives, and upload kickstart - as written about in our article Joomla! site backup package.
Once you have CuteFTP installed on your computer or laptop, you can set up a ftp connection to each website that you have. Each website connection can be set up to also "link" to a folder on your local computer or laptop so you can keep site specific extensions and files within a site specific folder on your computer or laptop.
The CuteFTP documentation explains very well all the features.