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 can enter the email address of the person or people that you wish to email, or click the button "Add Requester to..." which will add the email of the person who submitted the tripĀ  / 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 :