One of our team member (located in different region) has shelved changes in P4 with changelist 1234.
Now, if I want to see what files are modified snf what are the changes, how can I do this?
What is the P4 command that I should use to see the changes made by our team member?
p4 describe -S 1234 should to the trick, see the documentation on describe.
To see the file content you would unshelve the files into your workspace (assuming you have a workspace for the same project your colleague is working on).
Create a new (empty) changelist with p4 change (results in e.g. 2345), then use p4 unshelve (docu) to get the modified files to your workspace:
p4 unshelve -s 1234 -c 2345
If you don't want the modified files in your workspace any longer, you can p4 revert -c 2345 them.