Missing $ error <inserted>

You have not provided a full example but I would guess that you have

\documentclass[12pt, a4paper]{article}
\usepackage[latin1]{inputenc}

\begin{document}
\section{Goals}
\label{Goals}
Abbiamo già accennato nell'introduzione che uno degli 
obiettivi di questo elaborato è quello di focalizzarsi 
sullo sviluppo del software Model Driven a partire dalla 
primissima fase, di verifica dei requisiti, così da..
\end{document} 

which produces the error

! Missing $ inserted.
<inserted text> 
                $
l.10 ...ima fase, di verifica dei requisiti, così
                                                   da..
? 

The reason is that the encoding has been incorrectly specified as latin1 when your file is in UTF-8 If you declare [utf8] then

Why a math error? Well in UTf-8 non ascii characters take multiple bytes and ì takes 2, the bytes hex C3 AC . In latin1 encoding that you specified, each character takes a single byte so C3 AC is seen as two characters.

C3 is \~A

and

AC is \lnot which is a math operator seen here in text mode so generates the error.

This answer is a bit of guess, as you didn't post a MWE (Minimal Working Example).

I guess, that you missed to define the encoding used in your input file. I therefore added \usepackage[utf8]{inputenc} or in my case luainputenc.

At least, this MWE is working for me.

But as there is so much guess (e.g. I also removed the \labelsec-command, as I don't know, where it comes from. Maybe this is the root of your problem? Who knows.

\documentclass[12pt, a4paper]{article}
\usepackage[utf8]{luainputenc}

\begin{document}
\section{Goals}
\label{Goals}
Abbiamo già accennato nell'introduzione che uno degli 
obiettivi di questo elaborato è quello di focalizzarsi 
sullo sviluppo del software Model Driven a partire dalla 
primissima fase, di verifica dei requisiti, così da..
\end{document}