Go to your ‘index.html’ template and find the bit that says {$content}. Make a backup or keep a copy of ‘index.html’ in case you make a mistake. Then replace {$content} with this:
{if $smarty.server.REQUEST_URI == '/'}
Front Page Content
{else}
{$content}
{/if}
Where it says ‘Front Page Content’, place whatever you want to have as your static front page. (This could be a summary of what your site or blog is about.) Use regular HTML code for this part.
You will also need to put a link to your archives, so that your readers can find all your other posts.