Acquire the Spirit Calling Bell:

To summon Spirits you need to find the Spirit Calling Bell. This can be acquired from the Renna the Witch(Ranni) Witch that will appear to you after travelling to a specific Site of Grace(Church of Elleh).

Find Ashes:

After acquiring the Spirit Calling Bell from the Renna the Witch(Ranni), you must then find the Ashes of Spirit that you want to summon. These ashes can be found throughout the world of Elden Ring. Some of them can also be bought from certain merchants.

Where can i use the Spirit Calling Bell?

Once you both have the Spirit Calling Bell and Ashes, you must also need to be close to a Rebirth Monument to summon the Spirits. An icon will apear on the left indicating that Spirits can be summoned.