Your description is just as bad as before 
Script 1:
// left Indent: whatever, firstLineIndent: 8 mm
var curDoc = app.activeDocument;
if ( !app.selection.length ) {
var paras = curDoc.stories.everyItem().paragraphs;
}
else if(app.selection.length == 1 && app.selection[0].hasOwnProperty( "baseline" )) {
var paras = app.selection[0].paragraphs;
}
else {
alert("Something wrong with your selection!");
exit();
}
paras.everyItem().firstLineIndent = "8mm";
Script 2:
// left Indent: whatever, firstLineIndent: 0
var curDoc = app.activeDocument;
if ( !app.selection.length ) {
var paras = curDoc.stories.everyItem().paragraphs;
}
else if(app.selection.length == 1 && app.selection[0].hasOwnProperty( "baseline" )) {
var paras = app.selection[0].paragraphs;
}
else {
alert("Something wrong with your selection!");
exit();
}
paras.everyItem().firstLineIndent = "0mm";
Script 3:
// left Indent: 8 mm, firstLineIndent: -8 mm
var curDoc = app.activeDocument;
if ( !app.selection.length ) {
var paras = curDoc.stories.everyItem().paragraphs;
}
else if(app.selection.length == 1 && app.selection[0].hasOwnProperty( "baseline" )) {
var paras = app.selection[0].paragraphs;
}
else {
alert("Something wrong with your selection!");
exit();
}
for ( var i = 0; i < paras.length; i ++ ) {
var curPara = paras;
if ( curPara.leftIndent == 0 ) {
curPara.leftIndent = "8mm";
}
curPara.firstLineIndent = "-8mm";
}
If nothing is selected, all paragraphs are honored. If some text is selected, the paragraphs in the selection get the indent.
If this is not what you want, give detailed information, e.g. "Script 1 does not work, because … , also screenshot before, screenshot expected result" and "Script 2 … "