How to activate iFrame?

I honestly don’t know what version of WordPress I am using. I am still learning about WP.

Well, I tried to post iFrame embed in my post but it doesn’t work. When I did my research, what I found out that I have to active my iFrame which is located in the appearance tab.

My appearance tab doesn’t have iFrame/Plugin sub-tab. Now I’m o so confused. What shall I do?

Is there a simple and informative guide for me to be able to do what I want to do with my *******.wordpress.com blog? Or do in need a domain name and webhost?

Thanks for the help. Appreciate it.