Burp is designed to be used alongside your browser. Burp functions as an HTTP proxy server, and all HTTP/S traffic from your browser passes through Burp. To do any kind of testing with Burp, you need to configure your browser to work with it.
Confirm your proxy listener is active
First, you need to confirm that Burp's proxy listener is active and working.
Go to the "Proxy" tab, then the "Options" sub-tab, and look in the "Proxy Listeners" section.
You should see an entry in the table with the checkbox ticked in the Running column, and "127.0.0.1:8080" showing in the Interface column. If so, please go to the section "Configure your browser to use the proxy listener" below.
Press the "Restore defaults" button at the top left of the panel.
If the listener is still not running, then Burp was not able to open the default proxy listener port (8080).
You will need to select the table entry, click "Edit", and change the port number of the listener to a different number.
See the help documentation on Proxy Listeners for more details.
Configure your browser to use the proxy listener
Secondly, you need to configure your browser to use the Burp Proxy listener as its HTTP proxy server. To do this, you need to change your browser's proxy settings to use the proxy host address (by default, 127.0.0.1) and port (by default, 8080) for both HTTP and HTTPS protocols, with no exceptions. The details of how to do this vary by browser and version, please use the links below to find out how to configure your browser: