Syntax in HTTP requests and responses is automatically colorized to highlight interesting items, such as parameters in requests and HTML elements in responses. You can configure this behavior, and also the font, in message display options.
When syntax colorizing is enabled, the editor also displays mouse-over popups showing the decoded values of syntax items where appropriate. For HTTP requests, the popups perform URL-decoding, and for responses they perform HTML-decoding.
The text editor supports hotkeys for various common actions. These can be configured in the hotkeys options, and the default hotkeys relevant to the text editor are as follows:
At the bottom of the text editor is a search bar that can be used to quickly find expressions within the displayed text. As you type into the search box, the editor will automatically highlight matching items in the text. The "<" and ">" buttons can be used to move the selection to the previous or next match. The "+" button displays the following options:
Note that in addition to search highlights, some Burp tools apply their own highlights to requests and responses. For example, Burp Scanner highlights relevant parts of HTTP messages in its issue advisories. If you are not using the search function, you can use the "<" and ">" to move the selection between the tool-generated highlights.
Get help from other users, at the Burp Suite User Forum: