I put together this little GIF to show you what’s on my normal ADF altar. I will change it up depending on what I’m doing, but these three elements are usually present.
The candle represents Fire and and the Shining Ones. If I’m not home, this is often a little electric tealight or a red agate stone.
The bowl of water represents the Well of the Ancestors and the connection to the underworld.
The stone is my symbolism of the middle world (the place where we live) and the Axis Mundi that connects the upper world to the underworld. Sometimes this will be a leaf or plant depending on where I am.
I hope this helps to show how simple an altar can be.