Stylesheets cascading (CSS) are a simple Separation that used to separate the stylistic elements of a page such as provision of fonts and color page content such as paragraphs and images.
CSS also helps you have control over the layout and look of a web page. We can call this Separation of Content from Presentation.
If you don't understand CSS at all then you may decide not to use it for your site. However i would suggest that the advantages to be gained from using CSS, not just for Google, are well worth the time invested in learning it. Below are the points explaining why CSS is good for Google;