I put in an order to buy or sell some coins but the order did not get completed yet.
When you place orders at BX.in.th you can choose either a "Market Order" or a "Limit Order"; by default it will be set to Limit Order.
A limit order means that you set the price that you want to buy or sell for; a trade will not happen until another trader creates an order that meets your asking price.
While you are waiting for another trader to meet your price, the order will be called an "Open Order" and you can view it https://bx.in.th/funds/orders/ here. You can cancel an open order at any time and you will not be charged any fees, once you cancel an open order the funds will be returned to your available balance.
If you want your trade to get executed right away, you can use the "Market Order" type. This will automatically make a trade with any other trader based on whichever trader is available at that time.