How to Use Spells in Elden Ring

You will need to go to academy and fight Rennala.

And see her Rennala's Full Moon attacks.

You have to defeat Rennala.

And get remembrance of the full moon queen.

The grand library is unlocked.

The item says take it to the finger reader.

After that, you have to fast travel to the Roundtable hold.

Then make your way to finger reader.

You will need to convert remembrance to full moon.

Examine Rennala's full moon (70 Int).

You are unable to use it from the inventory.

After that, rest at grace and select Memorize spell.

Rennala's Full Moon Requires 2 slots.

Equip over a used slot to Occupy 2 slots.

And replace another slot with sorcery.

Top 3 slots  for right, below 3 for left.

Select one of the 3 top slots.

You have to choose any right hand Glintstone staff.

And select one of the 3 lower slots.

Choose any left hand Glintstone staff.

Right and left button to equip/Unequip.

You need to use the Up button to change spell.

If no glintstone staff is in hand, spell grays.

You have to choose any sorcery spell.

Staff in right hand, so press R1.

Use the staff in the left hand only.

Right hand empty, so R1 is fist attack.

Left hand has a staff, so L1 casts spell.

Get closer to the enemy.

Select Rennala's full moon spell.

Staff in right hand, press R1 to cast.

The shield can block spells.

Spells use up Mana (FP: blue bar).

If Mana is empty, the staff does no attack.

If no staff in right hand, R1 fist punch.

Down button to choose Cerulean tears.

Square to drink the selected potion.

Enough Mana to cast more spells.

Rest at Grace->Flasks to allot more Mana.

Flasks-> allocate flask charges.

You have to allocate more flasks for Mana.

See Rennala's full moon in Multiplayer.