Group and Ungroup Cells Manually

Group cells in order to select them as a unit or hide all but one cell in the group. (Cells are usually automatically grouped; manual grouping gives additional control.)

Select a range of cells

Mouse down on a cell bracket and drag to select a range of cells:

Group the cells

Choose Cell Grouping Group Cells/Group Together ():

Ungroup the cells

Click the group cell bracket and choose Cell Grouping Ungroup Cells/Group Normally ():

Double-click a cell in a group to hide the other cells in the group. Double-click a collapsed cell group bracket to open the group:
Cells typically group automatically: inputs with outputs, section headers with section contents, etc. You can turn off automatic grouping in a notebook with Cell Grouping Manual Grouping.