The SiteManager is your personal site library.
By default the SiteManager contains some useful ftp sites. You can add and remove sites and groups as you please. You can also rearrange the items and move them around with drag and drop after your own needs. From here you can easily connect to different ftp sites.
An alternative to use the SiteManager for connecting to a remote host is the quick connect command int FTP menu. This command open a small dialog which lets you connect to a host even if it's not in the SiteManager.
An other alternative is the recent connections command in the ftp menu. Here you have a list of the ten most recent visited connections. Note: this option can only be used for connections that exists in the SiteManager.