the tags are written in a lowercase letter.
Verify that there is only one space in between in words.
maximum five tags.
They are written in the line that is just below where you type the content of your post.
then click on the icon that says publication to upload your post to the network.
Write tags related to your post that already exist in the list or created by users for specific purposes. This way you will have more visibility. you can also search info here https://steemit.com/howto/@future24/tutorial-how-to-publish-an-article-at-steemit-quick-and-easy-guide-english-german