How to split cell text into multiline in table?

Package tabularx is your friend:

documentclass[twocolumn]{paper}
usepackage{tabularx}
    newcolumntype{L}{>{raggedrightarraybackslash}X}

begin{document}
    begin{table}
    centering
begin{tabularx}{linewidth}{|L|c|L|} 
    hline
textbf{Col1} & textbf{Col2} & textbf{Col3}  
    hline
This is a very long line of text & Short text & Another long line of text  
    hline
$pi$ & 1 in 5& Common in math
    hline
end{tabularx}
    end{table}
end{document}

If you want to control line breaks in cells, you can use the makecell command from the homonymous package. In addition, it has tools to add some vertical padding to cells:

documentclass{paper}

usepackage{array, makecell} %

begin{document}

begin{table}[thb]
centeringrenewcommandcellalign{lc}
setcellgapes{3pt}makegapedcells
begin{tabular}{|l|c|l|} hline
textbf{Col1} & textbf{Col2} & textbf{Col3}  hline
makecell{This is a very long line of text} & Short text &makecell{ Another long line of text}  hline
$pi$ & 1 in 5& Common in math
hlineend{tabular}
end{table}

end{document} 

Your wrong column alignment results from missing column delimiters (&) in your source code and can be fixed easily. This also fixes the broken vertical lines.

begin{table}[thb]
    centering
    begin{tabular}{|l|c|l|}
        hline
        textbf{Col1}  & textbf{Col2} & textbf{Col3}   hline
        This is a      &               &     % <===== note the empty cells in this line
        very long line &  Short text   & Another long   
        of text        &               &  line of text hline % <===== and in this
        $pi$          &    1 in 5     & Common in math  hline
    end{tabular}
end{table}

A less manual way would be to use the p column type, but you have to specify the column width and LaTeX will do the linebreaks for you, but your last cell will probably also break:

begin{table}[thb]
    centering
    begin{tabular}{|p{1.8cm}|c|p{2cm}|}
        hline
        textbf{Col1}                                                                & textbf{Col2} & textbf{Col3}                                                          hline
        This is a very long line of text &  Short text   & Another long line of text  hline
        $pi$                                                                        &    1 in 5     & Common in math                                                         hline
    end{tabular}
end{table}

Or you can use the multirow package. Load usepackage{multirow} in your preamble {anywhere between documentclass{paper} and begin{document}, and then you can do:

begin{table}[thb]
centering
begin{tabular}{|l|c|l|}
    hline
    textbf{Col1}                                                     & textbf{Col2} & textbf{Col3}                                             hline
    multirow{3}{*}{parbox{1.8cm}{This is a very long line of text}} &               & multirow{3}{*}{parbox{2cm}{Another long line of text}} 
                                                                      &  Short text   &  
                                                                      &               &   hline
    $pi$                                                             &    1 in 5     & Common in math                                            hline
end{tabular}
end{table}

Note that this aligns the columns vertically centered. The parbox{length} defines when your text should be broken.

I found the answer in the link below: https://pt.overleaf.com/learn/latex/Tables I hope it helps!