I think he means a bot. Bots can execute trading commands while you are away from a computer and can help with your trading strategies (but not replace them!). There is a steep learning curve to using them, and you have to find a good bot with positive feedback and reviews first. Go slowly!
So you mean using a HTTP API to sell coins type bot or one that hooks into the HTML on the page from say GDAX and presses
the "Sell button" if your are logged in and the price flops.
Me is second to no one when it comes to bots but i think i would do that using a chrome extension
Bots are all over GDAX doing the buying and selling and if you watch you can see something like
$15,001 10.0100000
$15,001 9.0100000
$15,001 5.0100000
$15,001 4.0100000
//No sell so lower price and cycle again
$15,000 10.0100000
$15,000 9.0100000
$15,000 5.0100000
$15,000 4.0100000