User Level: 
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D7 - Fields - Configuration - User Entity Reference Field - Add Field

1. Add User Entity Reference Field

On the Manage Fields tab:

Add New Field Section

Label field = Enter the name of your new field. Note that a machine name is automatically generated from what you type in this field. If you wish to edit the machine name, click its corresponding Edit link (characters in this field must be all lowercase, alpha-numeric only).

Type of Data to Store select field = select Entity Reference.

Form Element to Edit the Data select field = select either Checkboxes/Radio Buttons, Select List, OG Reference, Autocomplete (Tags Style) or Autocomplete. Our example uses a Select List.

Click the Save button.

D7 - Fields - Configuration - User Entity Reference Field - Add Field Settings

2. User Entity Reference Field Settings

You will be redirected to the Field Settings tab.

Target Type select field = select User.

Mode select field = leave it set at Simple.

Target Bundles checkboxes = select all of the content types you want to display in the reference field.

Sort By select list = select A Property of the Base Table of the Entity.

After making a selection in this field, new fields will appear beneath it:

Sort Property select list = choose Name.

Sort Direction select list = choose Ascending.

Render Views Filters as Select List checkbox = check this.

Click the Save Field Settings button.

D7 - Fields - Configuration - User Entity Reference Field - Add Other Configs

3. Other User Entity Reference Field Configurations

You'll be redirected back to the field's Edit tab.

Here you'll have some basic settings regarding the appearance and quantity of this field.

Label field = this can be changed at any time.

Required Field checkbox = if this is a field that must be filled out, check this box.

Help Text text area field = enter optional help text here, if desired.

Default Value text field = allows you to set a default value for this field.

Field Template select field = provides integration with Display Suite.

Number of Values select field = the number of entries that you can add to this field.

Click the Save Settings button.

D7 - Fields - Configuration - User Entity Reference Field - Position Field

4. Position User Entity Reference Field Configurations

You'll be redirected back out to the Manage Fields tab.

You can position your field as desired by grabbing the field's mover handle, at the left of the field title, with your mouse. Drag it up or down as desired.

Click the Save button.

D7 - Fields - Configuration - User Entity Reference Field - Add Data

5. Add Data to Field

Go to the content type that has this field on it and edit or create a new node.

Locate your field within the submission form.

Enter some data.

Click the Save button.

D7 - Fields - Configuration - User Entity Reference Field - Field Display

6. User Entity Reference Field Display

The User Entity Reference Field will display.