When you click the Send button easyDnc will send only the currently selected line and stop. You can repeatedly click the send button to Single Step through your program.
When drip feeding you might experience a tool break. When you're ready to restart you would not necessarily want to go right back to the start. You'd probably want to select a specific line and run from that point. Or, if you weren't sure about a specific area of your program, you might want to single step through it.
On the previous page you saw that when you click the Send button new buttons - [Pause] and [Stop] - appear. No need for us to explain what those buttons do. But interesting is that during drip feeding at full speed you can hit pause and switch the mode to single step - for example if you wanted to single step through a section of your program that you wanted to observe closely - and at any time switch back to full speed machining.