You're "tapping a permanent for mana" only if you're activating an activated ability of that permanent that includes the symbol in its cost and produces mana as part of its effect.

Mana Reflection affects any permanent you tap for mana, not just lands you tap for mana.

Mana Reflection doesn't produce any mana itself. Rather, it causes permanents you tap for mana to produce more mana. (This is different than seemingly similar cards like Heartbeat of Spring and Gauntlet of Power.) If the permanent puts any restrictions or riders on the mana it produces, as Pillar of the Paruns and Hall of the Bandit Lord do, that will apply to all the mana it produces this way.

Mana Reflection doesn't cause permanents you tap for mana to produce one extra mana -- rather, it doubles the type and amount of mana that permanent would produce. For example, if you tap Mystic Gate for , it will produce instead.

The effects of multiple Mana Reflections are cumulative. For example, if you have three Mana Reflections on the battlefield, you'll get eight times the original amount and type of mana.

If you have Mana Reflection on the battlefield and tap a permanent for mana, but another replacement effect would change the type and/or amount of mana it would produce (such as Contamination, which says "If a land is tapped for mana, it produces instead of any other type and amount"), you decide what order to apply those effects in. In this example, applying Mana Reflection first and Contamination second would result in ; applying Contamination first and Mana Reflection second would result in .