‘After these things Jesus revealed himself again to the disciples at the Sea of Tiberias, and he revealed himself in this way.'
‘After these things Jesus --.' This is a typical loose Johannine connection (see especially John 6:1). For reference to ‘The Sea of Tiberias', see also John 6:1, the only other reference to the Sea under that name in the Gospels. Both these factors support authorship by John.
‘Jesus revealed Himself again', following the ‘revealing' described earlier in chapter 20. The verb indicates a sudden, unexpected and temporary revelation. One importance of this narrative is that it confirms that there were Galilean appearances as mentioned in Matthew and the Marcan ending, and that the disciples spent some time there between the resurrection and the ascension.