Macintosh HD - Data filled (vs Macintosh HD)

I have read that Macintosh HD - Data (vs Macintosh HD) is a read only partition that is established to enhance security.

Coming from a lay man, how does it improve security and how to I access and look into its contents. This is because I am using a 2015 Macbook Air 13' inch with 128GB storage and Macintosh HD - Data has already taken up 98.9 GB of my precious storage.

How am I suppose to approach this problem at the same time educate me on the gist of having Macintosh HD - Data.

Thanks peeps. Cheers.