Landing page, thank you page, subscriber page, Confusion

I need some help please.

If you have been following my WA post from last week, you know that I have now got an autoresponder. I got it all set up according to the way I thought I needed it to be, then some confusion has happened.

I created a campaign with 6 emails. My first email is a Welcome email. All my emails for my campaign are created on AWeber.

With my opt-in I used the basic default Thank you page that I personalized a bit.

Then once they get the default thank you confirmation page, 15 minutes later they get my first email that is the Welcome email with my giveaway.

My confusion comes in when all the training I see they say to create your own Thank you page on my website and use that URL instead of the AWeber one.

All the examples I see of thank you pages include the giveaway here and thanking you for joining. Isn't this page just part of the opt-in only? These thank you pages look like my 1st email of my campaign. Did I mess this up?

Also I created a landing page as an opt-in to join my email list, but I created it in AWeber not on my site. I tried creating a page in my website but it looks just like a blog post even after I got rid of the widgets, and header and footer.

What is the best thing to do here? If I use a free plug-in like Elementor or WP Landing pages do I have more ways to change the look?

Then of course what do I do with the done landing page. Right now I shared my AWeber landing page on FB and Pinterest. What else can I do with it?

I realize there are a lot of questions in here, but I am just spinning a bit and need a bit of guidance.

I hope you can help me figure out what I am mixing up.