Check out example codes for "html table stack overflow". It will help you in understanding the concepts better.

Code Example 1

<style>
table {
width: 100%;
}
td {
  border: 1px solid #777;
  padding: 10px;
}
td:first-child {
  width: 30%;
}
</style>
<table>
  <tr>
    <td>a</td>
    <td colspan="3">b</td>
    <td colspan="3">c</td>
  </tr>
  <tr>
    <td>a</td>
    <td colspan="2">b</td>
    <td colspan="2">c</td>
    <td colspan="2">d</td>

  </tr>
</table>

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