how does glowstone interaction work, can enemies do anything

Glowstone is a hot potato — whoever controls it at the end of their own turn eats it: Glowstone kills itself and deals 5 damage to all units that player controls. Enemies have several ways to interact.

The loop: play it to your Base, pay [A][A] to Empower it, then activate "Disempower this, [T]" to hand it to an opponent — it's recalled to their Base (still exhausted, no longer empowered). At the start of their Ending Step (Rule 317.1) its trigger fires, and in the following cleanup all their units with Might 5 or less die; Might 6+ survive and heal (Rule 323.5.3b + 317.2.b–c). It hits units at Bases and Battlefields alike.

What the enemy can do:

• Remove it — it's a targetable Gear at their Base (Rule 148.1.a.3). Kill/bounce it in their Main Phase before their Ending Step and the trigger never fires. They can even respond to the pass ability itself with a Reaction spell; if Glowstone is gone when it resolves, the hand-off fails.
• Pass it back — on their Main Phase they can pay [A][A] to re-Empower it, then use its own ability to hand it to you (or a third player), who then takes the 5 at the end of their turn. They can't use the ability on a non-empowered Glowstone — "Disempower this" isn't payable when it isn't empowered (Rules 442.1.a.1, 203.3) — so they must empower first.
• Once the trigger is on the Chain, it's too late — killing Glowstone in response doesn't stop the 5 damage; only the "kill this" is ignored, the damage still resolves (Rule 359.3.e.6). Only damage-prevention-type effects save their units.