Buy orders are the best way to show your interest in a nugget that is not yet at the price you want!
Concretely, you indicate the price you are willing to pay from the horse's file. If one of the holders accepts your offer (or if the market price reaches it), the transaction takes place automatically and the memorabilia joins your stable.
The amount of your purchase order is reserved in your account as long as your order is active. This means that if you place an order of €10 on a memorabilia, then these €10 are blocked until your purchase is made. And if you change your mind, you can obviously cancel it at any time: the amount becomes immediately available again.
In short: you offer your price and let the magic happen.