You've not told us whether you're using an email client (such as Outlook, Outlook Express, Thunderbird or Windows Live Mail) or a web-based mailing system. The instructions vary slightly but, basically, to send an email with an attachment you (unsurprisingly) need to look for a button to click which is labelled 'Attach', ''Attach file', 'Attachment' or something similar.
Once you've clicked the button you'll see a dialogue box, which enables you to navigate to the location of your file. You then simply need to double-click on the file name. (Alternatively single-click and then click on the button which is labelled 'Attach' or, occasionally, 'Open').
You'll then see the name of your attachment appear at the top of your email. Clicking 'Send' will send both the email and the attachment with it.
To send an email to multiple users, simply type all of the addresses in the 'To' field, separated by commas.
It's also possible to create a 'group', containing all of the email addresses, so that you only need to select the group name as the outgoing address (instead of typing out all of the names individually). However the method for doing so varies depending upon which email system you're using. (If you require further details, please post again, telling us which program - or web-based service - you use to send your mail).
Chris