You can add meta keywords and descriptions easily into your Joomla web page.

Login to your Joomla backend and go to "Content" > "Article Manager" from the main menu.

Click on the article that you wish to add the meta keywords and descriptions.

On the right side of the screen, you will see "Metadata Information". Click on it to see the fields.

Enter your meta keywords into the keywords field and the description into the description field and you are done!