<td>要素の使い方・サンプルコード

<table class="table">
  <tr>
      <th>A</th>
      <th>B</th>
      <th>C</th>
  </tr>
  <tr>
    <td colspan="2">1</td>
    <td>2</td>
  </tr>
  <tr>
    <td>3</td>
    <td colspan="2">4</td>
  </tr>
  <tr>
    <td colspan="3">5</td>
  </tr>
</table>

.table {
  width: 300px;
  border-collapse: collapse;
}
.table th, .table td {
  border: 1px solid lightgrey;
}
.table td {
  text-align: center;
}

<table class="table">
  <tr>
      <th>A</th>
      <th>B</th>
      <th>C</th>
  </tr>
  <tr>
    <td rowspan="3">1</td>
    <td rowspan="2">2</td>
    <td>4</td>
  </tr>
  <tr>
    <td>5</td>
  </tr>
  <tr>
    <td>3</td>
    <td>6</td>
  </tr>
</table>

.table {
  width: 300px;
  border-collapse: collapse;
}
.table th, .table td {
  border: 1px solid lightgrey;
}
.table td {
  text-align: center;
}

<table class="table">
  <tr>
      <th>A</th>
      <th>B</th>
      <th>C</th>
  </tr>
  <tr>
    <td rowspan="3">1</td>
    <td colspan="2">2</td>
  </tr>
  <tr>
    <td>3</td>
    <td rowspan="2">5</td>
  </tr>
  <tr>
    <td>4</td>
  </tr>
</table>

.table {
  width: 300px;
  border-collapse: collapse;
}
.table th, .table td {
  border: 1px solid lightgrey;
}
.table td {
  text-align: center;
}