You may ring a Beckoning Bell to become the host to a maximum of 2 "Guests" players who have rung their Small Resonant Bell.
Beckoning Bell becomes available after you gain 1 Insight,
Small Resonant Bell requires you to gain 10 Insight.
You may ring a Sinister Resonant Bell to become a hostile guest in another host's world or you may be summoned by a Chime Maiden. Up to two hostile guests are allowed.