I'll let you know about all I know on the subject. Got 30 seconds ?? 😀
You (lessee) go to someone who has an a/c for lease (known as the lessor), and arrange the term. These can be any length, but the one's I've seen were 6 months, and annual terms. You agree to pay for 'x' amount of time. Be it 300, 600, 1,000 hours. Whatever is in the agreement. You pay so much per month, and so much per hour. Depending on the deal, the lessor covers replacement/overhaul of things like the engine, main, tail rotor blades, etc at the recommended o/h or replacement time. You pay for inspections, on condition items, oils, fluids, consumables, any damage you cause, those sorts of things.
Leases can pay off if you have a flying contract that will cover the minimums you pay, and it's a relatively short-term job. If you are leasing for spec., well that's when you can lose your shirt if you don't fly the minimums. An example: you agree to lease for 6 months, and for say 300 hours. Let's say they charge you 2,000/month, and 350/hour, so you guarantee to pay $117,000, not including fuel, oils, etc. If you only fly 100 hours, well you get the idea. Each lessor will write their deals a little differently, and cost differently, but they pretty much work the same.
Hope I helped.
Cheers