What is free cash and advantages of it

What is free cash can I use it for trading and advantages

Imagine you brought 100 rs for trading and with 20 rs you bought something and 80 rs are still available to you, this is free cash of yours, you can use it at any place where you want , advantage of always mainting free cash is that it helps you when you need it most like you want to average something, market gives high correction , thats a time to make great money, it can always be made with free cash only, thats why it is always suggested that maintain always free cash with you