Hidden behind the lyrics

Rich girl 

Released 2004

• The song was written in reaction to children who aspire to be wealthy as an adult. Which is reported to be her childhood desire after becoming a music sensation. Which I'm sure we can all agree she did.
• Stefani used a lot of Japanese ladies in the song video because she fell in love with the area known as "Harajuku" while touring in Japan. The location is believed to be highly stylish within the clothing of teenage girls, which appealed to her eyes and provided them with a platform to shine on - The Rich girls' video. The "Harajuku girls" are mentioned inside the song's lyrics.

Hollaback Girls 

Released 2004 

• The song's title, "Hollaback Girl," alludes to one of the cheerleaders who screams in the background. Gwen Stefani is claiming to be the queen bee on this team, leading the cheers with the Hollaback gals at her disposal.
• "Get in really close."  Stefani says followed by "Aw, so kawaii" in the start of the music video, referring to her backup dancers as "cute." This is in reference to Stefani's love of Japanese culture, which was mentioned earlier in the article. The Japanese language is a recurring topic in Stefani's work. Through her videos as well as her lyrical content.
• Stefani (from Rolling Stone, June 16, 2005): "I did the whole record, but I knew I didn't have my attitude song - my 'this is my history, f--k you because you can't erase it' song. I knew I wanted a song like that."

Cool 

Released 2005

• “This song is about Gwen Stefani's ex-boyfriend and No Doubt bandmate, Tony Kanal. They dated for eight years before breaking up because Kanal needed "space." The song is about how both of them moved on and how through the ups and downs, over the years, they became really good friends. Stefani found the "love of her life," Gavin Rossdale, whom she married in 2002, so she and Kanal were "cool" as friends. He later married the actress Erin Lokitz; Stefani and Rossdale divorced in 2015.” (from: https://www.songfacts.com/facts/gwen-stefani/hollaback-girl).
• Stefani references "Harbor Boulevard" in Fullerton, California, where she attended California State University Fullerton as a late teen/early adult.

What are you waiting for?

Released 2004

• The meaning behind the song itself refers to Stefani’s fear of leaving a group that is like family to her to pursue a solo career - “Naturally I'm worried if I do it alone… Who really cares cause it's your life… You never know it could be great…”.
• Stupid ho represents her because that's what society sees her as. Or at least how she felt seen by the environment around her at the time. 
• She also associates with her doubts about being a mother at 35 as she feels that her time is running out as a woman to bear children. She's under pressure to pursue a “hot artist” career but also hopes to be a mother to conform to society.