in SharePoint. Also you can check out my previous posts on:
document.write('Hello World !!!');
Copy the text file and put it inside the C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS\STYLES folder.
Open the page where you want to add Content Editor Web Part and edit the page. After that in the edit mode click on Add web part and from the Ribbon select the Media and Content web part category and select Content Editor web part and then click on Add.
Click on OK.