Your resume is arguable the single most important part of the application process. A well-organized, relevant resume will set you up to get an interview, while a poor resume will get completely lost in the sea of applicants. This is a fairly modern concern, as job postings now get thousands of online applications a day.
Using a functional resume format is beneficial when you have gaps in employment. The functional resume highlights honors and achievements more than work experience. It lists your skills and other attributes that make you a good employee at the top of the resume. It is important to fill the gaps in employment with experiences that helped you grow. Volunteer work, continuing education, and other projects you worked on during that time are all great options. Be sure to use a positive tone while describing the gaps in employment and be confident about them when interviewing later.