Seriously? When writing a new post, right next to the huge textarea you type, you have a box named "Publish" - the bottom entry in that box is "Publish immediately" with a nice "Edit"-link next to it. The rest should be self-explanatory.
You can try on Dashboard click All Posts. under Title Posts click Quick Edit, change date with future date, click Update. click All Posts once again. if the right steps you will see Schedule Posts after Published
you can schedule posts months in advance, i tend to do a week for blogs. when you are writing your post, instead of publish immediately click and a dropdown box will appear showing the current date etc, then if you want to publish in that month just change the date and time for your post and click ok, then click schedule and that's it. You post will be published on that date and at that time