The exact procedure you use to compose a new message will depend on your email
client but here I will illustrate the procedure using Outlook Express. Click on
the create mail icon

A new message window opens up with the address bars, subject line and message
body. I have completed the fields and will explain the main points.

The address field entries show from,to,cc,bbc fields this can be changed
(in OE) by clicking view all headers.
The from field is visible because this client is configured to receive mail for
multiple email accounts and so it is also possible to send mail from multiple
email accounts. A drop down bar (right not visible) lets you change the from
address.
The to,cc,bcc fields can ether be filed by typing the address manually or by
selecting the recipient from the address book. If you use the address book then
the display name appears and not the full email address (Anne bailey above).
Any of the fields can contain multiple email addresses each address is separated
by a semi colon .
The cc (carbon copy ) field is used to copy the email to others that should be
aware of the email but not need to act on the email.
The BCC (blind carbon copy) field is used to copy the email to others that
should be aware of the email but not need to act on the email. None of the email
recipients are aware of email addresses contained on the bcc line and so it is
used to keep email addresses confidential. See
To,cc,bcc for more details.
As a matter of email etiquette all emails should have a subject line (spam
filters will often block emails that don't have one).
The above message is using html format which you can change using the format
menu. If I do that you can see in then screen shot below that the text editing
option bar disappears.

Other message options like adding attachments, spell check, read receipt are
available using the quick icons or the top menu options.
When you have finished click send and the message will be send immediately. If
you want to edit the message further you can use the file menu to save the
message in your drafts folder.
Adding Attachments
Compose the message as normal and then click the attach icon (outlook express)

Navigate to the file you want to attach and click it a new field appear under
the subject line with the attachment displayed. You can repeat the process and
add multiple attachments.

You should not exceed 5MBytes for all files and be aware some attachment types
(.com,.exe etc) may be filtered out by the email servers so it is best to only
send text/document/spread sheet/power point type files.
Other types of file should be zipped.