A table that looks like a paper table

Tables in LaTeX involve two nested environments with different jobs. The inner tabular builds the grid of cells. The outer table makes that grid a float, so it can carry a number, a caption, and a label, and so LaTeX can place it where the page has room. Add the booktabs package for the horizontal rules and the result looks like a table from a published paper rather than a spreadsheet screenshot.

\usepackage{booktabs}
\begin{table}[htbp]
 \centering
 \caption{Results on the test set.}
 \label{tab:results}
 \begin{tabular}{lcc}
 \toprule
 Model & Acc. & F1 \\
 \midrule
 Baseline & 0.81 & 0.79 \\
 Ours & 0.87 & 0.86 \\
 \bottomrule
 \end{tabular}
\end{table}

The outer environment

The [htbp] argument lists where LaTeX may place the float: here in the text, at the top of a page, at the bottom, or on a separate page of floats. It tries them in that order, and granting all four keeps the table from drifting far; the mechanics are explained in where floats actually land. \centering centers the grid horizontally. The \caption prints the numbered caption, and by convention table captions go above the table, unlike figure captions, which go below. \label must come after \caption, because a label records the most recently issued number, as covered in captions and labels. With the label in place, Table~\ref{tab:results} in your text always prints the right number.

The inner grid

The {lcc} after \begin{tabular} declares one column per letter: l is left-aligned, c is centered, and r would be right-aligned. Three letters means three columns, and every row must supply exactly that many cells. Within a row, & separates cells and \\ ends the row. Text columns usually read best left-aligned, while short numeric columns are commonly centered.

The three rules come from booktabs. \toprule opens the table, \midrule separates the header row from the data, and \bottomrule closes it. These replace the plain \hline command and come with correctly tuned spacing above and below, which is most of why the table looks professionally set. Notice what is absent: no vertical lines, and no rule between data rows. The booktabs style deliberately omits both, and the reasoning is laid out in three-rule tables.

Practical notes

The most frequent beginner errors are a mismatch between the number of & separators and the declared columns, and a forgotten \\ at the end of a row, both of which produce confusing error messages pointing at the next line. If you would rather not hand-count cells, build the grid visually with the table generator and paste the result into your document.