Monopoly rules
The official answers to the rules everyone has been playing wrong since childhood.
Most Monopoly arguments are between the printed rules and a house rule someone inherited. Each answer says which is which.
Free Parking
Officially, nothing happens. Free Parking is a resting place. There is no money in the middle, and no rule anywhere in the rulebook that puts any there.
The jackpot is the most common house rule in the world, and it is also the main reason games run for four hours: it pumps money back in and stops anyone going bankrupt. If you want a game that ends, drop it.
Auctions
If you land on an unowned property and choose not to buy it, the banker must auction it immediately. Everyone bids, including the player who declined, and bidding can start at any amount, even £1.
This rule is in every edition and is skipped in most games. Playing it properly makes the early game far sharper, because passing on a property no longer keeps it off the board.
Jail
Get out by rolling doubles, paying £50, or playing a Get Out of Jail Free card. You may pay before rolling if you prefer.
You get three attempts. Fail all three and you must pay the £50 and move the number you rolled on the third try.
You still collect rent while in jail. Late in the game, sitting there is often the safest place on the board.
Building evenly and the housing shortage
You must build evenly across a colour group: no second house on one property until every property in the group has one. Selling works the same way in reverse.
There are only 32 houses and 12 hotels in the box, and that is a rule, not a component limit. When the houses run out, nobody can build until some come back. Buying hotels to free up houses, or refusing to, is a legitimate and brutal tactic. If several players want the last houses, the bank auctions them.
Passing Go
Collect £200 every time you pass or land on Go. Landing exactly on Go pays £200, not £400. The double is a house rule.
Rolling doubles
Roll doubles and you move, act on the square, then roll again. Roll doubles three times in one turn and you go straight to jail without moving to the third square.
Going bankrupt
If you cannot pay, you sell buildings back at half price and mortgage properties. Still short, you are bankrupt and out of the game. Owing a player, they take everything you have, mortgaged properties included. Owing the bank, all your property goes to auction.
Questions
Is there really no money on Free Parking?
Correct, there never has been. It is the most widespread house rule in the game, and the one that makes games run longest.
Do I have to auction a property I do not want?
Yes. Declining to buy triggers a compulsory auction, and you may bid in it yourself.
Can I collect rent while I am in jail?
Yes. Being in jail stops you moving, nothing else.