The Eval function is used to define one-way binding (read only).You can use the Eval method when the control will only display values.
The Bind function is used for two-way binding (read-write).You can use the Bind method when users can modify a data value – that is, for data edit/update/view scenarios called two-way databinding.
Chandradev's Blog 
realy it is very simple for understanding.thanks.
You are welcome.