I have been a certified technician since 2001 and have provided technical services to family, friends, and many other individuals here and there. I don’t have a business license and tax ID, however, that is going to change soon. Can I add this work experience to my resume? If yes, how and where on the resume should this information be expressed?
By all means, Yes! Whether or not you have a business license and tax ID number, your experience can be listed on your resume.
If your unpaid experience is something you were doing while unemployed, insert it into your Experience section without mention of it being unpaid. You can refer to yourself as "Independent Technician." When doing this, be sure the heading of the section does not imply that everything listed in the section is paid experience. For example, instead of Employment History, say Experience.
If you have no gaps in employment, your unpaid experience can be listed in a separate section called Additional Experience.
In either case, if your unpaid experience is highly relevant to your job objective, and you don't have similar experience listed under your paid experience, highlight it as one of the qualifications you list in your Summary of Qualifications section.