If you need to send an email from inside your trip request you will start by going to any tab where you are going to open a trip request /  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 trip  / 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 :

You will see the email in the Email Audit Log.  This gives you a snapshot of the actual email.  You may see this by hovering on the envelope next to "Email Sent by:"