Login to your wordpress account:
websiteaddress.com/wp-admin
the top black menu is a quick way to do useful things in WordPress.
on the Left is a W in a circle (wordpress link), then a HOME button and the site name. Then indications of how many updates are available, how many comments and then the [ + New link ] to add new Posts.
The left hand menu also allows you to list and add new posts.
If you are currently an AUTHOR – you can only add posts. Your admin will setup Categories for these. Each post belongs to one or more categories and the selection of the category agrees with the Menu items in the Updates item of your main menu.
Your site Admin will help you to add new categories and may advise you to keep categories list to an absolute minimum.
Posts, Post Categories and Pages can all be menu items but as an Author, you can not add to menus. You admin will do this for you. Simply assign it to an existing Post Category and your post will be accessible from the menu.
Or, assign it to the Admin category, and Slack the post URL (the link near the top of the page that appears under the title when you have added the title) to the admin. Admin posts do not appear on your public site, usually.