[pdftex] new to pdftex

[M. Kalidoss]

Dear Sir,

I have MikTeX and it contains the PDFTEX program.

I am completely new to pdftex program.  When I attempt
to use the ordinary *.tex file, it starts complaining as

\documentclass{article}
unknown control sequence etc. 

Will someone enlighten me as to how to start using it. 

I prefer to use TeXtelmeXtel tex editor.  How to use it
to run pdftex?
Many thanks in advance.
Yours sincerely,
Dr. M. Kalidoss, M.Sc., M.Phil., Ph.D., F.A.S.I.,
Reader in Physics,
St. Joseph's College (Autonomous),
Tiruchirapalli - 620 002
India
Phone: 91-431-721 438 (C)
             91-431-458 820 (R)
FaX    : 91-431-701 501