You summon spirits of the dead and they appear in unoccupied spaces that you can see within range. Spirits are undead creatures possessing Incorporeal Movement Choose one of the following options for what appears:

• One spirit of challenge rating 2 or lower
• Two spirits of challenge rating 1 or lower
• Four spirits of challenge rating 1/2 or lower
• Eight spirits of challenge rating 1/4 or lower

Each Spirit is considered undead, and it disappears when it drops to 0 hit points or when the spell ends. The Spirits arrive after 1d4-1 rounds

The summoned creatures are friendly to you and your companions. Roll initiative for the summoned creatures as a group, which has its own turns. They obey any verbal commands that you issue to them (no action required by you). If you don't issue any commands to them, they defend themselves from hostile creatures, but otherwise take no actions. If you lose concentration you lose control  of the spirits and they are no longer friendly. At the end of their turn, they vanish and return to their graves or haunts, unless they are destroyed or controlled. You can dismiss the spirits before the spell ends and the spirit return to their graves or haunts.

While your DM is the final arbitrator of whether a creature is a spirit or not, most undead undead creatures possessing either of the special traits Incorporeal Movement or Amorphous are spirits

The GM has the creatures' statistics. Sample creatures can be found below.

At Higher Levels. When you cast this spell using certain higher-level spell slots, you choose one of the summoning options above, and more creatures appear: twice as many with a 5th-level slot, three times as many with a 7th-level slot, and four times as many with a 9th-level slot. When you cast this spell using a spell slot of 4th level or higher, the challenge rating of the spirits you summon increases by 1 for each slot level above 3rd.

Sample Spirits

Sample Creatures of for Casting the Spell at Higher Levels