My question about that On-page SEO And keyword ds

I have a question when we have do on page SEO and research keyword with low Keywords density . Than I found a keyword phrase example - what is CMS in the website design (with keyword density 39). Can I use this title of web page (website design and CMS) and same use as focus keyword and other on page activity.

Please :pray: give me answer and what is solution will I have used low Keywords density and actractive title and heading

I am very confusing

I have working this website

your student