Step-by-step guides are processes surrounded by content - not the other way around. So there are two best ways to go about creating your guide from scratch are:

• Create a giant list of all the important steps to take. Working backwards for the end result is usually the best way to accomplish this. You can then group tasks thematically by stage into Sections afterwards or drag and drop them into the right spot.
• Create the most critical Section(s) right away then fill them in with tasks one at a time.