How to add and edit posts in WordPress
Posts, also referred to as articles, can be added and edited from the admin panel of your WordPress. After you log in click on the Posts menu on the left. On the page that opens you'll see a table with the existing posts; the table has several columns showing various information related to the post (e.g. title, author, category, etc.). With the exception of the column for the title you have control over which columns are to be included in the table. To hide/display columns click on the Screen Options button in the upper right corner and mark/unmark the respective checkbox(es).
You can also mass edit posts. To do this mark the checkbox that's next to the title of each post that you want to edit, select Edit from the Bulk Actions drop-down menu (there's one above the top left corner of the table and another one below the bottom left corner), then click on the Apply button that's next to the drop-down menu. Some options will appear; you can use them to assign the posts to a category or categories, you can change the author, status and format of the posts, you can enable or disable comments and pingbacks, and you can make the posts sticky on the frontend. After that just click on the Update button that's below the options.
You can perform actions with each individual post by hovering the mouse pointer over its row in the table and clicking on one of the buttons that appear under the title. You can make a quick edit, you can move the post to the trash or you can go to the edit form by clicking on the Edit button. You can also go to the edit form by clicking on the title of the post.
To add a new post click on the Add New button that's in the top left corner of the page. The add and edit post forms are basically the same one. At the top there's a text field where you can type or edit the title of the post. Under it there is a built-in text editor with which you can type and format the content of the post. After that you just need to click on the Publish button. In case you're editing an existing post the same button will be labeled Update. There are also some blocks on the add/edit form with additional settings. More blocks can also be made visible by editing the screen options. For more information on these blocks and settings check out the tutorial on managing the post settings and blocks on the add/edit post form in WordPress.
For more details and screenshots on adding and editing posts you can also read the tutorial on how to manage posts in WordPress.