UI Modes
Playa 2.1 introduces two new “UI modes” – alternative interfaces for your Publish pages. Each are available to both normal fields and FF Matrix cells.
Drop Panes

This is the classic Playa interface. It is composed of two panes. On the left is a list of each of your available entries, and on the right is a list of your selections. To select an entry, simply drag it from the left pane to the right, dropping it in your desired sorting position.
There are two drop pane UI Modes: “Drop panes with filters” (pictured above) and “Drop panes”. They are identical except that the former also includes a filter bar on top, which lets you filter the left pane by Weblog, Category, Author, Status, and Keywords, as well as sort the entries by Title or Date, in Ascending or Descending order. These filters only affect what you see in the left pane, making it easier to locate entries, should you be dealing with a large number of options.
Multi-select

If you have no use for custom sorting in the Publish page, a simple multi-select input might be adequate.
Select

If you only want authors to be able to select a single related entry (like EE’s built-in Relationship fieldtype), choose the Select UI Mode.
Regardless of which UI Mode you choose, you can still take advantage of all of Playa’s other features – multiple weblog selection, searchability, and the full range of template tags and params.