If it says you have to increase content then you have to fill your website with content first. Moreover, a new website cannot apply for Google Adsense, your website has to be at least 6 months old but 3 months will also do just fine. Then there are some other things which you have to keep in mind, like to provide a contact page, a terms and services page, about us page, disclaimer page and policy page.These are some important things which you have to keep in mind before you apply for Google Adsense.
The content on your website should be top notch and not copied from any place else. Finally, your content should not be related to sexual and abuse in any form. After you are all done then apply for Google Adsense and you'll get it.
For more information regarding Google Adsense you can read their Terms and Services.
I hope this helps.