If you need to send an email from inside your trip request you will start by going to your Main tab / click on Your Trip Requests / click on the blue trip number to open the request form (the one shown below is a sample trip) / scroll to the bottom of the request / you will then see the Send Email button - all of those steps look like this :

Now that you have clicked the Send Email button a box will open up - you need to enter the email address of the person or people that you wish to email / type your subject line (I normally like to add the trip number in the subject line) / type your message / now click the Send Now button - those steps look like this :