First step when making web updates is to log into your site. Your user name and password will be provided .
DO NOT LOOSE IT
Both username and password will be the same for Login Into Nice Page also.
Once you have successfully logged into your Joomla website you will be presented with the standard Joomla UI.
The only section of any interest for your is the "Articles" section highlighted below.
Click the "Articles" tab and it will produce a list of all your "Articles/Pages" on your site
Select any "Article" and it will start the editing login process with NicePage, select "edit With NicePage" to begin.