Hi, I am new in web designing. Here, I want to place new post on my home page periodically. Now, I have to go design mode and removing old content then adding new content. If i can add post like blog post - it would be better to me. I also want to preserve my old content instead of new. I created my site by html and css. Please help me.
For what you are looking at you would need a CMS system such as Wordpress and they use PHP and MySQL as well as CSS and HTML. If you just want to use update the code then you can use a PHP include
Your site is static and its never possible to update/add content (or new content) just like blog post. All blog site are installed in Dynamic mode so that we can add content without going to SOURCE CODE. If you want to overcome with this problem you should build a DYNAMIC website having ADMIN panel, so that you can enjoy posting just like BLOG. It would be better to prefer CMS for this purpose like WordPress, Joomla, Drula, Magento etc. All the best !!
I'd suggest modx as its very easy to use with basic html and css, then move onto something harder if it does not suite your needs.