What's the process of playing a gear, how does equip work, when can I play a gear and equip it, where can the unit be when I equip a gear?

Short version: Play the gear to your Base (it enters ready), then use its Equip ability — an activated ability usable in your Main Phase during an Open State — to attach it to any unit you control, wherever that unit is.

Playing a gear. Pay its cost; it goes on the Chain, finalizes, and resolves immediately — units and gear skip Execute/Pass, so opponents get no reaction window to the play itself (FAQ #8333). By default gear enters your Base, ready (Rules 149.1–149.2), and can be played on your turn in an Open State.

How Equip works. Equip is an Activated Ability: [Cost]: Attach this gear to a unit you control (Rule 818.1.c.2). It behaves like a spell without a card — it goes on the Chain, so the state closes and opponents can respond with Reactions to it (FAQ #9560). Standard timing is your Main Phase, Open State, and not during a Showdown (Rules 151.2, 381) — so it's neither an Action nor a Reaction (FAQ #1120). Once the gear is attached its rules text goes inactive, so you can't use that Equip ability to move it off (Rules 718.2, FAQ #2139); you can still pile multiple gears on one unit (FAQ #6479).

Timing after playing. Yes — you can play a gear and immediately Equip it in the same Main Phase, as long as you have the resources for the Equip cost and the state is Open with no Showdown running. Quick-Draw is the exception: it grants Reaction inherently and auto-attaches on play (Rule 819.1.d), letting you play and attach at Reaction timing.

Where the unit can be. Anywhere you control it — your Base or a Battlefield you control; Equip has no location restriction on the target unit. If you equip a unit at a battlefield, the gear becomes located there through the Attach action (Rule 152.2); if that unit later dies, the gear stays at that battlefield and gets Recalled to your Base at the next Cleanup (Rules 457, 149.3).