Hi flippaaaa
Welcome to the server.
To buy from a chest shop (at the /mall for example), punch the chest you wish to but from. Then in chat you’ll see it asking you to type how much you want to buy.
In chat, type:
/n <amount>
With the amount you wish to purchase. So if you wanted to buy 3 x mending books, you would type:
/n 3
Good luck and happy shopping.