1st thing to do for on page is website audit. It helps you to check all the issues on your website. Then 2nd thing is keyword research which helps you to target relevant audience of your niche. Then 3rd comes on page changes.
On page Tasks:
1. Meta Tags
2. Img Alt Tags
3. Heading Tags
4...
Organic results are those when you search something relevant to your niche on Google and search engine shows the top results on the 1st page. That results are called organic results or organic traffic.
For track your website traffic, you just need to add Google Analytics code in your website head section. It will help you to track all the organic, direct, social and referral traffic.