Open the document you wish to share. In the top right of the screen, click “Share”

You should get a screen like this:

In the box that says “To: Name, group, or email”, you can enter the individual email addresses of the people you want to share with. You will either need to enter the entire email address of the person and immediately follow it with a semicolon, or you can click on the person from the list that appears below.

Their email address will look like this whenever it has been selected:

You can also specify what permissions the users will have with the document here. If you click the pencil icon to the right of the user list, you will be presented with the following options:

If desired, you can include a message to send to the user(s) receiving the file. Click “Send” whenever you are done.