Spells cast from the ring use normal actions and no components.

Many magic items allow the user to cast spells. The general rules for this are on p. 141 of the DMG, under the Spells subsection of Activating an Item:

Some magic items allow the user to cast a spell from the item. The spell is cast at the lowest possible spell level, doesn't expend any of the user's spell slots, and requires no components, unless the item's description says otherwise. The spell uses its normal casting time, range, and duration, and the user of the item must concentrate if the spell requires concentration.

(emphases mine).

Beyond these rules for magic items, casting a spell follows the rules in the Player's Handbook; generally, the character casting the spell takes the Cast a Spell action on their turn.

Here's what the Ring of Spell Storing says about casting the spells in it (DMG, p. 192:

While wearing this ring, you can cast any spell stored in it. The spell uses the slot level, spell save DC, spell attack bonus, and spellcasting ability of the original caster, but is otherwise treated as if you cast the spell.

Let's look at two examples of stored spells being cast:

1. Fireball stored in the ring at 3rd level by a 10th Level School of Evocation wizard with a save DC of 16
2. Magic Circle stored in the ring at 5th level by a 11th level Cleric with a save DC of 17.

Fireball, cast from the ring by a 3rd level Sorcerer (save DC 14):

• Will require one action to cast (same as the spell)
• Will do 8D6 damage; the original casting wizard's Empowered Evocation feature will not apply since it is not one of the characteristics that the ring lists as being 'stored'.
• Can be used with Quickened Spell by the casting sorcerer, since that falls under being "treated as if you cast the spell".
• Will have a save DC of 16, from the original caster.

Magic Circle, cast from the ring by a 19th level Fighter:

• Will require one minute to cast (same as the spell).
• Will not require any chalk or other material components, even though that is normally required.
• Will have a duration of three hours (base duration plus two extra hours for using a 5th level slot).
• The fighter has no spellcasting ability, and thus no spell save DC, but the Magic Circle will have a save DC of 17.

The Ring of Spell Turning states:

In addition, if you roll a 20 for the save and the spell is 7th level or lower, the spell has no effect on you and instead targets the caster, using the slot level, spell save DC, attack bonus, and spellcasting ability of the caster.

So this means, the spell does not originate from you even when you have returned it, but instead you merely redirect the target. This means that it is as if the cleric used command on themselves using the word "Flee."

This is the effect of the "Flee" command word:

Flee. The target spends its turn moving away from you by the fastest available means.

Therefore, the cleric is commanding themselves to flee from themselves. This is a contradiction -- you cannot possibly move away from yourself. However, the command spell also stipulates:

If the target can't follow your command, the spell ends.

So in this case, the spell would end immediately, since the cleric cannot follow their own command.

This also means that if the spell had a concentration requirement, such as polymorph or banishment, they can willingly end concentration because it is still their spell, they just shot themselves with it instead of you.

Finally, the Ring of Spell Turning cannot return a spell that does not target only you. If command was cast at a higher level such that it targets you and someone else, then you cannot return it. You would also not have advantage on the saving throw.