How to send mail right?

Question

Hello everyone! I have a question and i hope to be helped.
My question is i have just rent a host and domain for that host. Now i wonder about Mail Sending ?
EX:
1.
I rent the host and they  give me information about a lot thing: Plesk panel information,Mail Account information, Domain and FTP information...

2.
When you login inside Plesk panel to manage hosting .there will a tool "Create Mail Account" for you create one or plenty mail account.

3.
Your private Account in yahoo or gmail.

So my question is when i create the website for my custom.What mail account i use to user Feedback to admin of that website.Cause i often see a lot company or something when they send mail for me, their mail account look like:[email protected] or [email protected] and otherwise when i apply for somecompany their mail account like belove.Please help me solve it!