How do you manage your gmail account to send huge emails?

You want to create a group.

1. Go to your contacts (in Gmail, click down arrow or click here)
2. Move your mouse into the left column (where the Google Hangouts widget rests). It will expand the contents there and reveal a link called “New Group”.
3. Enter a name for this group.
4. Select the newly-created group from the left .
5. Click the add contact button to add contacts.
6. Just start typing and separate all contacts with a comma or click “add” to add one or more at a time.

Now, when you create a new email, rather than start typing email addresses in the “to” field, type the name of that new group you created. It will email everyone you have added to that group.

I re-read this question and realized that your question might be more simple than this. While the above is ideal if you send emails to a large group on a regular basis. However, if you are really just asking if you can chose your contacts any other way besides “typing the first letter”, the answer is yes.

1. Click “Compose” to create a new email.
2. Click the word “To” rather than the space next to it.
3. A window will appear where you can perform searches on contacts and see full lists that match the search, etc.
4. Select a contact by checking the checkbox.
5. You can keep performing searches and selecting the contact via checkbox.
6. When you are done, click the “Select” button.

@hominid has it, except there is a Check All box at the top so no need to check each one individually. If you want you can uncheck any that you don’t want to include.