Start by using the status bar icon, the Options item on the SyncPlaces menu or the toolbar button:
On the Server tab, enter the details of your web server (requires WebDav - see Support section) or ftp server:

Select the protocol to use (http or https for a web server, ftp for an ftp server, file for a shared folder). Enter a hostname or IP address (e.g. ftp.yourname.com or www.yourname.co.uk). You can optionally add a port number if you need it as well (e.g. www.yourname.co.uk:8080). The user and password fields are optional but will be needed if you've (sensibly) protected your web/ftp server with a password.

On the Synchronisation tab you can choose to synchronise either using a JSON formatted file or an XBEL file. JSON is ideal for the storage of all the bookmark information from the new Firefox Places system (e.g. tags, queries, and annotations) and with the compression option will result in the fastest synchronisation. XBEL is simplistic, has larger files and slower to use, but is ideal if you need to synchronise with Firefox 2, or other browsers/services. Note that if you do choose to receive/import XBEL from another source (i.e. not SyncPlaces) you will probably lose all the new features (see the Support section for more info).
In either case you can also choose to synchronise your passwords and list of password exceptions. This will send a separate file to the server. This file is automatically encrypted for safety, so you'll need to provide a password (key) for this (see below).
Unless you are using the 'file' protocol, all the paths on the rest of this tab must begin with a '/' and are the names of files that will be created on the server. If you are using the 'file' protocol then any valid path will work, with the exception of UNC paths (e.g. \\my_server\my_folder\syncplaces.xml) where you will need to map a drive instead.
If you synchronise using JSON, then you can also select the 'Send XBEL' option to also send your bookmarks in XBEL format. This is ideal for transforming your bookmarks into a web page for remote access from any browser. There are additional options on the Advanced tab to help with this styling.
The 'Send HTML' option will also send a web page of all your bookmarks. This is for people who don't wish to deal with XBEL. Note that this is generated by the 'Export HTML' option in Firefox so SyncPlaces has no control over the formatting or the content.
The last item on this tab is the password required to encrypt/decrypt passwords/exceptions that are synchronised. This must be entered or the synchronisation will fail. You can choose which encryption method to use on the Advanced tab.
On the Actions tab, clicking the Send button will convert your bookmarks and (optionally) passwords into your selected format, and send them to your server. But note that if you have the Send safely option turned of then it will do a receive and merge before the send:

From another browser, enter the same server details and then click the Receive button. The bookmarks/passwords are then downloaded from your server to your browser and merged with your existing ones. Note that when passwords are merged, if two entries are identical apart from the password, a dialog prompt will appear asking you to choose which password to keep.

When you click Receive, before your current bookmarks are changed they are automatically saved first (passwords are not). So you can easily restore them using the Restore button. You can also use the Backup button to take a manual backup at any time, and restore this backup using the Restore button. You can also sort all of part of your bookmarks at any time using the Sort button:

Finally, you can export your bookmarks into a local XBEL formatted file or import an existing XBEL file. Any valid XBEL file may be imported as long as it is in UTF-8 format. XBEL files from older/other bookmark synchronisers should import just fine. Also you can make use of the 'Select folder to synchronise' option to export/import a single folder.
