Delete line in vi

What should i do when i delete a line in vi?

It's what i'm doing right now

1. Open up the terminal alt + ctrl + t
2. vi a.txt
3. I move my cursor to the line which I wan to delete, then what key-combination is should use to delete line in vi editor ?

Pressing dd will remove that line (actually it will cut it). So you can paste it via p .