Please guide me to add a slider on homepage and some content and then

Hi there,

you can use a GP Page Header and add any Slider or other content Short Code within its Content area. Then assign this to your Blog page.
Here is the page header documentation:

https://docs.generatepress.com/collection/page-header/

What exactly do you want to appear below the navigation?

i want to put a slider, and then few posts lists based on categories. Something like on http://www.digital-photography-school.com 's homepage.

I just want that on homepage. And not on posts/pages.

i am a little new to wordpress. On blogger there used to be a simple drag and drop widget. But in wordpress i don't see an option to place a widget/slider/code on home page, Above the posts

I think the Page Header method that David mentioned is your best bet.

You can create a new Page Header, and add a widget area into the content area. If you use a plugin like this, you can add a widget area to the Page Header using a shortcode: https://wordpress.org/plugins/widget-shortcode/

Let me know if you need more info :)