You should search this forum before posting questions; I did search on email+cell and got a few results :
For example, this post answer does almost exactly what you want to do.
EDIT following your edit :
use an IF
condition.
Something like this :
var cellG = ''
if(cell.indexOf('D')!=-1){ // = if you edit data in col D
cellG = sheet.getRange('G'+ sheet.getActiveCell().getRowIndex()).getValue()
// add more condition if necessary and/or send your mail (cellG contains the value in column G of the active row
}
Logger.log(cellG)