I know this is a beginner\'s question, but I\'ve been searching online and all I can find are \"free website templates\" that I can download.
The question is: How can I
There are two places you can do this:
The two basic approaches to this are includes (simple) and full template systems (powerful).
For a runtime include system, the popular choice is PHP's include function. An alternative is SSI. You can even use a C preprocessor.
Template systems include PHP's Smarty.
My weapon of choice is Template-Toolkit, which can be used via Perl at runtime and comes with ttree for use at build time.
Less sane options involving making the client do it and include frames and JavaScript.