I am using notepad++ for php coding.
I don't have any problem with format set up using Encode in ANSI.
However when I use Encode in UTF-8, either I have a strange character at the top or not showing anything.
Q1. Am I supposed to use ANSI? Q2. Why do I am not able to display anything when I use UTF-8
My sourse code for the header is following.
<html>
<head>
<title>Hello, PHPlot!</title>
</head>
Is that because I am not using UTF-8 in the header?
It's probably a Byte Order Mark. You can use the 'Encode in UTF-8 without BOM' mode in notepad++.
This question has some helpful information about using UTF-8 with PHP. You will also (as you suggested) need to set the content type in either the header or a meta tag in order for the browser to interpret it correctly.
It sounds like you are using UTF-8 with a BOM (which has issues) and your server is failing to specify the encoding correctly.
IIRC, BOM is unavoidable in Notepad, so I would suggest using a better editor. I'm fond of Komodo Edit myself.
(Also note, that a Doctype is required in HTML documents)
As Tom Haigh says, it's probably the BOM. It's not necessary for UTF-8 encoding, so you can safely leave them out.
However I should point out that PHP has very weak support for UTF-8 - be prepared for a bumpy ride. Take a look at this page for some details on problems you might encounter.