By A Web Design
The easiest way to add video to a WordPress page is to do it via YouTube. To be able to do you will need a YouTube account. Once you have a You Tube account, upload your videos to your You Tube account. Subsequently, You Tube will deliver these videos to your WordPress posts - on demand.
Once your videos are uploaded, Open your You Tube account in your Browser. Select the appropriate video you wish to display within your WordPress Blog Post, then copy the URL of the You Tube video and its associated Embed code provided by You Tube as shown in Diagram 1.

Diagram 1
To embed this video into a post(s) in WordPress 3.X.X login to WordPress as administrator, by simply entering the url_of_your_website/wp-admin in your Browser. Enter the appropriate username and password {which was provided while installing Wordpress} and then click on Log In as shown in Diagram 2.

Diagram 2
After logging in as WordPress Admin, the WordPress dashboard page opens as shown in Diagram 3.
The Dashboard provides access to different WordPress functions and features.

Diagram 3
In the left menu, locate the link Posts. Click Posts. From the drop down menu that appears click on Posts as shown in Diagram 4.

Diagram 4
Click the Title of the post as shown in Diagram 5 or click Edit to open the post in its editable mode.

Diagram 5
Once on the post, insert the cursor where you want place the video as shown in Diagram 6.

Diagram 6
In Visual view, Paste the URL of You Tube Video directly on the post as shown in Diagram 7.

Diagram 7
On the right hand side publish box, click Update to save the changes made on the post as shown in Diagram 8.

Diagram 8
In the front end of website, the video has been successfully inserted on the post at the cursor position as shown in Diagram 9.

Diagram 9
You can alternatively use the - embed code - copied from You Tube, which is an HTML code snippet. In the WordPress post editor ensure that you are switched to the HTML editor as shown in Diagram 10.

Diagram 10
While the editor is in HTML mode, set the cursor where you want the video to be displayed and paste the codespec copied from You Tube to embed the video as shown in Diagram 11.

Diagram 11
On the right hand side publish box, click Update to save the changes made on the post as shown in Diagram 12.

Diagram 12
In the front end of website, the video has been successfully inserted on the post at the cursor position as shown in Diagram 13.

Diagram 13
If you want the video to be centered on the post then in visual view, place the cursor where you want the video to be displayed. Click the center alignment button as shown in Diagram 14.

Diagram 14
The cursor moves to the center of the post as shown in Diagram 15.

Diagram 15
Click HTML tab, the codespec to align text to center appears as shown in Diagram 16.

Diagram 16
Replace the space provided between the p tag with the HTML Embed code of video as shown in Diagram 17.

Diagram 17
On the right hand side publish box, click Update to save the changes made on the post as shown in Diagram 18.

Diagram 18
As compared to Diagram 13, the video is centered on the post as shown in Diagram 19.

Diagram 19