How do I enter the quantity?

The quantity determines how many stocks, contracts or lots you bought or sold for the specific trade. 

A stock trader enters the number of stocks bought/sold for the trade.

A Forex trader could either write down the number of lots (eg. 2.5) or the number of contracts (eg. 250,000). 

We do not have a mandatory way of entering quantity. There is no right or wrong here and you can choose a format that makes sense to you.