vhdl code for 4 bit bidirectional universal shift register using behavioral style of

Simple enough, you have the full data sheet describing the functionality.

First write the external module interface, then define all the registers you need.

Then write the equations that define how a registers transitions from state to state based on input signals and its current value.

You must surely have had some exposure to the VHDL language syntax and semantics so far in you course, I assume?