How to point default domain to /home/site/public_html/index.html?

Hey folks I am new to ubuntu (I know the cringe) and running servers (that I 100% manage) just got digitalocean server for free and figured I move my web hosting to my own self managed to learn about it for fun

My intended goal is: To host 1-3 websites using different domains with let's encrypt and free cloudflare dns. From what I gathered this is pretty good thing to use as I have used cpanel and wanted something like that as I am comfortable with that.

My Problem: I succesfully managed to install virtualmin with root (which not sure if that is bad?) so far my domain http://foxumbit.com/ has the Apache2 default page I tried putting files in public_html and it's not updating. I found the apache index.html file but when I try to overwrite it I get this in filezilla

Command: put "C:\Users\Alexa\Desktop\New folder (2)\images\pic03.jpg" "/var/www/html/images/pic03.jpg"

Error: /var/www/html/images/pic03.jpg: open for write: no such file or directory

Error: File transfer failed

(which sames for every image/html file)

(but I can transfer to /home/foxumbit/public_html/~)

My goal is to have like

/home/foxumbit/public_html/index.html @ Foxumbit.com/index.html

/home/OtherWebsite/public_html/index.html @ Otherwebsite.com/index.html etc...

Any suggestions on what I need to do would be helpful :) Thanks.