Entity drop-down list (ajax)
This special type of field is designed to build a one-to-many relationship. This type of field is analogous to the field type "Entity", but has a number of additional settings for displaying a list of records in the form.
First of all, this type of field is suitable for displaying a list with a lot of data. Since the data is loaded into the list by an ajax request, displaying the list of related records itself does not slow down the program.
In the field settings, you can specify which fields cab be used to search for entries in the list, and also configure the display of the list itself.
Please note: that you can use HTML in the Heading template, as well as the type of the Image field.
The main feature of this field is the function of transferring values from the selected record to the current form. In the field settings you indicate which fields you want to transfer:
When you select an item from the list, the field values will be automatically transferred to the current form.
Display records according to condition
Clicking on the name of the field you have the ability to set filters for the selected entity. These filters will be applied when creating a list of records.
Also, on the "Condition" tab, you can manually specify the data selection condition. This condition is embedded in the MySql query when generating a list of records.
Example 1: select all entries with a certain status.
e.field_217 in (68,69)
217 is the ID of the status field in the selected entity. (68,69) - the ID of the status.
Example 2: select all entries where the assigned user is the same as user in the current form.
e.field_219 = 
219 - ID of the field with the type users in the selected entity. 312 - field "users" in the current form.
You can also use the [field id] construct in the condition to use the value from the parent record.
Example 3: compare the dates
The  field is a type of Date field with a calendar. The date from the form is passed as a string Y-m-d, so the field values must be taken in single quotes
Entity Multilevel Dropdown
This type of field is an analogue of the "Entity drop-down list (ajax)" field with the difference that the list of values is formed on the basis of the selected value from the parent entity.
Then several lists will be displayed in the entry form, depending on the nesting of the entity.
Each value in the list will depend on the selected value from the previous list.