Hi again Aigars,
I am trying to develop my website now therefore I kinda ask lots of question. Thank you for your assistance!
BTW, i am kinda confuse with post and pages. The thing that i confused is, why is your pages (italy, france,spains etc) have a different post. i want to learn that. when i enter https://colorlib.com/travelify/ it shows the example of the pages but not how to do it…
Where can i learn?
Those pages in the upper menu are actually Categories, they are just used as pages in menu. You can do the same thing via WordPress Menus.
WordPress Menus allows you to link to any page in your website or even to other resources.
Haha. I am really confused. I wanted to do it like this (https://colorlib.com/travelify/category/spain/) but i can’t figure it out. I have problem to set home page to the main page with the slider too…
I am as confused as you are 
Here are category page on your website: http://flynngoodholiday.com/category/uncategorized/
You can create as many categories as you want and add links to them via WordPress Menus.
Additionally you can hide these categories from home page via Theme Options → Homepage Post Options.
This is how Travelify Demo is created.
Let me know if this helps.
YAY…i made it. finally. thanks for your assistance Aigars!
I think this might be the last question (lol), how do i click Home button and it goes to the main page (http://flynngoodholiday.com/) instead of going to this page (http://flynngoodholiday.com/home-2/)
I don’t know how you got it done now but you should create WordPress menu via Appearance → Menus. And add your homepage URL as Custom Link. You can arrange, rename your pages from there.
More info on Custom Menus you will find here.