The dj mode does automatically queue related tracks which are by related artists, but are generally ordered by similarity to that track.
If no usable similar tracks are found, the script will automatically try to find similar artists in your library and find a random top track from a random similar artist.
For example, if you play Blue Train, it look for these
similar tracks in your library.
If it can't find any usable tracks, then it will automatically look for
similar artists, pick a random similar artist that is in your library, then pick a random top track from that artist.
If it still can't find any usable tracks, then will reduce the time restrictions and try again, after a few tries and it can't anything it will eventually just pull a random track from your library so the queue does not run out.
so to sumarize,
dj-mode: queue similar tracks to now playing using the last song in the now playing list as the seed
last.fm node: shows the similar tracks to the currently playing song
artist: shows top tracks for playing artist, expand to show your favorite artists (expand for their similar artists)
tags: shows top popular tracks for playing tag (using its genre), expand to show your favorite tags (expand for those tags artists)
users: shows weekly, overall, and recommeded artists and tracks
and so on
you don't need the dj mode enabled to use the last.fm node or vice versa
the dj mode does the queueing, the last.fm node itself just lists the tracks/artists, but does not queue anything or generate actual playlists.