Just sitting (Jpn Shikantaza) is a form of objectless meditation in which we just sit with life as it is. There is no endpoint or goal and no thought of enlightenment. Just let body and mind drop away. In normal life, there is no need to strive to be mindful but instead engage all activity with the same mind.
The group is hosted by Zen student Andy McLellan but there is no teacher or leader here. I may be able to answer questions on meditation but am no guru. If you want to obtain formal teachings on Sōtō Zen, I can greatly recommend Treeleaf Zendo online which is run by acredited Zen teacher Jundo Cohen. However, practitioners of other Buddhist traditions and none are also welcome. Just sitting requires no belief in reincarnation, karma, gods, devas, pixies or Harry Potter although also works just fine if you do believe in any of those things.
You should probably be aware that there will be a Buddhist shrine in the room but there will be no bowing or chanting unless everyone really wants to do that. There may be optional metta verses at the end but these just involve sending good wishes of health and happiness.