The Ancestral Infuser is a mid to late-game block used for advanced infusion recipes involving spirits.
To correctly set it up, the ancestral infuser must be placed on top of a Block of Soul Sand; both must be surrounded by air. No blocks can be adjacent or caddy-corner to the Infuser or Soul Sand and both must be in low light or complete darkness. If everything is set up correctly, the orb on the Infuser will start floating and waving around. If the orb is just floating in place, your infuser setup is incorrect.
In order to power the table, the Soul Sand must be supplied with Spirits from a Bottle of Spirits; keep in mind, each bottle yields 8 spirits. Craft the bottle, then right click the Soul Sand with the bottle- it should turn red, and right clicking the Soul Sand will display how many spirits it contains. This process will gradually make the orb in the middle of the Infuser appear redder.
Every recipe requires MORE than 8 spirits to be present in the table.