Are you working in Windows? Using the standard picture viewer?
Go to your My Pictures folder, find the pic you want, click on it and then look on the bit on the right of your screen and under File and Folder Tasks you will find E-mail this file. Click on that. You will get a little window asking you if you would like it compressed (or something), say yes or OK. You will then get a new e-mail window up with the file in the attachments slot. Select Save attachment under the File menu of the e-mail. If you only want to send one pic then send this e-mail. If you want loads of pix on one mail then close this e-mail.
It sounds complicated, but it's not. Once you've done one you can get seriously hooked (yes, I am that sad).
Repeat as many times as you need to until all the pix you want are compressed. Finally, create the e-mail you want to attach the pictures to and attach them.
I know this because I found out how to do it yesterday and spent HOURS compressing pix which I thought I might want to send sometime!
I found it helped if I created a new folder on the desktop, (which I called small pix) so I could find them easily.