So you have website, but have no ideas where to start SEO. then here comes low Hanging Keywords of website.
These keywords are keywords that are getting impression on google, but no clicks.
So by little on-page SEO, you can rank these keywords.
How to find these keywords.
Step 1: Go to Ahrefs Site audit.

Go to Aherfs site audit. Then Login to aherfs account. you can use your gmail account also.
Step 2: Go to create project

Click on create icon.
Steps 3: import or add your project

Import your website using google search console. after importing your site, then Ahrefs crawl your site for technical error and give you overall site audit.
Steps 4: Click on website
After clicking on website it give you overall performance in google search engine, such as organic keywords, organic traffic
Step 5: click on organic keywords

click on organic keyword tab. It gives you list of keywords that are getting impression and organic position on google.
Steps 6: Choose keywords that rank between 4 to 15 Rank Position

Choose keywords that ranks between 4 to 15 position. These are the low hanging fruits keywords of your website. By making some on page SEO. you will rank for this keywords
Steps 7: Do basic on-page SEO like Title and meta description change
Now you have low hanging fruits keywords, analyse the webpage that have these keywords. Then Update your title tag, Meta description and heading with these keywords. And see your ranking after few days.
You will rank for those keywords.