house is on the market

No, that sentence is perfectly correct. Your "friend's house is for sale on the (housing) market".

Thanks, Mame.

I thought the house was built on the market.

No, it wouldn't be built on the market. It would be for sale on the market. Think of the stock market, only it's a housing market.

Thanks again, Mame.

'on the market" means to be for sale.

A house "on the market" means that the house is with others that are also for sale.

The "Housing Market" is used to describe the real estate business of selling homes. You may hear that the Housing Market is not good in the US right now.

You can also have a "Buyers Market" - where the buyer has many homes to choose from because there are more homes than buyers.

A "Seller's Market" is good for the seller because there are many buyers and not many homes, so the homes sell quickly.

Thanks, SULLYFISH66