There are two approaches to sending an email with attachments. The first is to share one or more items using an app that created or manages them and the second is to compose an email in the Mail app and attach one or more items.
Here is how to send an attachment starting with an app that created or manages the items you wish to share.
Apps that can be used to share items as email attachments include Pages, Files and Photos. In the documents view of Pages, or in the Files or Photos app, browse the folder or album from which you want to share and locate and double tap the select button near top right. (In some apps, you may need to double tap on a More button to reveal the select button.) Now select one or more items by double tapping them.
Next locate the share button near bottom left and double tap.
Alternatively, if you want to attach just one document, you can locate the document and then swipe up until you hear share and double tap.
A share sheet will pop up at the bottom of the screen. The share sheet includes many sharing options. Either slide your finger to locate the Mail button which should be near the centre of the bottom of the screen or swipe right to this button.
Double tap and a Mail compose screen will appear. The item or items that were selected will be attached to the email. Complete and send the email as usual.
The second approach to sending attachments begins with the compose button of the Mail app. Compose an email in the usual way. When you have finished writing the message body do the following. First double tap with one finger until the insertion point is at the end of the message.
On an iPhone, explore above the right of the keyboard for the expand toolbar, button and double tap. This will reveal a toolbar and VoiceOver will probably be focused on insert drawing, button.In some cases the toolbar will already be expanded and you will hear insert drawing. Swipe left to hear the other options. These will include insert attachment, button and insert photo, button. If you choose insert attachment, you will land in the Files app where you can navigate to the desired folder and add an attachment. I think items can only be added singly this way but you can return to the insert attachment button to add further items. If you choose the insert photo button you will be able to select a photo from recent photos or from all photos. If you select all photos, you will have the full view as in the Photos app. If the document you wish to share was created or edited recently, then it will probably be simpler to locate the document by using the recents tab in the Files app.
On the larger iPad screen, the toolbar is always present above the right of the keyboard, so feel at top right of the keyboard for the insert drawing button and then swipe left to discover the other toolbar buttons.
Finally, send the message as usual.
The toolbar will also be available when you are replying to an email.
Note that if a document has been created in apps which use their own formats, such as Pages, Numbers or Keynote, you may need to export the document into a different format for it to be easily accessible to all users. PDF is often the most appropriate choice.