To create a post for YouTube, click the Create a Post button from the left rail of your Dashboard and select the YouTube account.
Enter details about the video in the text field. Then, add your video by either clicking "Add Media" to upload from your computer or by dragging and dropping the file onto your post.
Once the video is uploaded, you can add a Title and edit the Privacy Status: Public, Private or Unlisted. You can also upload a custom thumbnail if you wish.
Once you're satisfied with your post, you can either schedule your post for later by clicking the clock icon and then "Schedule now" - or, you can click Post Now to send the post immediately.