In one-way sync, files are copied only from a primary location (source) to a secondary location (target) in one direction, but no files are ever copied back to the primary location. Replication and Backup (=Mirroring) are one-way sync methods in ViceVersa.
In two-way sync, ViceVersa copies files in both directions, keeping the two locations in sync with each other. Synchronization and Consolidation are two-way sync methods in ViceVersa.
You might set up a one-way sync to backup your files to the network, for example, where ViceVersa will copy every new files from your computer to the network but never to copy files in the other direction (from the network to your computer). When files are deleted from your computer they are also deleted from the network.
You might set up a two-way sync between a desktop and a laptop computer, for example, where ViceVersa will copy the newest version of any file it finds to the other location, overwriting any older versions of the same file. This is a good way to sync if you work with the same files on both computers and want to make sure you always have the most recent version of every file you have worked on, no matter which computer you are using.
During a two-way sync, ViceVersa will alert you whenever it finds a conflict, which typically occurs when a file has changed in both locations since the last sync. Rather than overwrite either of the files that have been updated since the last sync, ViceVersa will show the conflict and you can decide which version to keep.