"This is how I found out the solution" in one word
Solution 1:
You could go with rationale:
Definition of rationale
1 : an explanation of controlling principles of opinion, belief, practice, or phenomena
2 : an underlying reason
Solution 2:
Personally, I would use:
Reasoning
the drawing of inferences or conclusions through the use of reason.
Solution 3:
Method [meth-uh d] /noun
- a procedure, technique, or way of doing something, especially in accordance with a definite plan
Source: Dictionary.com
Solution 4:
You might consider simply using the heading
Procedure
1 a: a particular way of accomplishing something or of acting
2 a: a series of steps followed in a regular definite order
- Merriam-Webster
Procedure is commonly used as a sub-heading when writing a research paper. For instance, in the field of Psychology, by APA guidelines, the section called "Method" has the following sub-sections:
- Participants
- Materials
- Apparatus
- Procedure
For more on this kind of formal "procedure" writing, see the APA guidelines at Hamilton.edu
Procedure fits especially well with a portion of writing that explicitly goes through the steps required to accomplish something, as exemplified in your sample in the question:
...first navigating to the File menu and then... [etc.]
Solution 5:
Proof
evidence or argument establishing or helping to establish a fact or the truth of a statement.
Source: Oxford