Simply drag a step from Elements Panel (1) and drop it to an empty space on the canvas into necessary Responsibility line and Milestone column. Milestone (2) what step will be put to will be outlined with purple, and Responsibility (3) - with green:

As a result, step will be put into proper place:

If you have some connected steps on the canvas already (4), you can drag a step from Elements Panel and drop it directly onto their connector (5):

In this case step will be inserted between both already connected. Direct connector between them will link first existing step with newly added, and it's properties (conditions, actions, etc) will remain unchanged (6). New connector from added step to second existing will be added automatically (7):

You can just type step name in the Steps Tree (8). Submit the name by clicking "Enter" and Manual step with given name will be added automatically after previous step or Start one (9).

Also you can insert step before or after currently selected by clicking proper buttons on steps tree toolbar:

You can import steps structure from the Excel / Open Office Calc / etc. or online spreadsheet.

• Copy text containing proper data in proper format into clipboard.
• Click "Import Tasks" button above steps tree (10):

• Proper popup will appear (11)
• Select "CSV - Plain Text" Data Type (12)
• Paste copied data into the proper field (13)
• Change column delimiter (if necessary, 14)
• Click "Import" button:

• After several seconds import process will finish and show proper notification (16). If any problems happen, warnings will be shown there (17):

• All valid steps will be added to process automatically according to their structure that depends on predecessors of each step.

You can import steps structure from the CSV file.

• Click "Import Tasks" button above steps tree (10)
• Proper popup will appear (11)
• Select "CSV - File" Data Type (18)
• Select proper file (19)
• Change column delimiter (if necessary, 14)
• Check "1st row is header" (20) checkbox if CSV file contains header
• Click "Import" button

All valid steps will be added to process automatically.

Select a step by clicking or outline several steps with mouse:

Right-click on selected steps and select "Copy" item in context menu (23):

Then right-click on the canvas and select "Paste" item in context menu (24):

Steps will be pasted to the canvas:

Select a step by clicking or outline several steps with mouse.

Use "Copy" keyboard shortcut (Ctrl+C for Windows/Linux, Command+C for MacOS).

Then use "Paste" keyboard shortcut (Ctrl+V for Windows/Linux, Command+V for MacOS).

Steps will be pasted to the canvas.

Select a step by clicking or outline several steps with mouse.

Right-click on selected steps and click "JSON Export" item in context menu(25):

Copy selection from "Export JSON" popup:

Open other necessary process in Process Builder. Right-click the on the canvas and select "Import JSON" item in context menu (26):

Step(s) will be pasted to the canvas:

Select a step by clicking or outline several steps with mouse.

Simply drag and drop step(s) into necessary place on the canvas. Green dashed placeholder (27) will show where step will be placed. Red dashed lines (28) will appear automatically to assist with alignment of steps.

Select a step. Drag the markers (29) to resize step.