Choose the post you want to have it sticky in the front. See the image, and tick "stick this post to the front page". This will make your post stay in front page.
There is a better way - to use WordPress as a CMS - with a frontpage - the best way is to create a Page rather than a post, and set this as the frontpage in the settings (reading).
If you want a static frontpage create the page first, then go to Settings/Reading and switch from latest posts to "Static Page", then select that page. Or if you want it to update with the latest post go to Settings/Reading and where it says "Blog pages show at most", change it from the default 10 to 1
Under settings go to "read", and then select post and choose the post you want to have on the first page. You can also get a plugin called "sticky post", then under the post at the bottom check for "sticky post" Let me know if it helps Dan