How can I free some space on my MacBook Pro from junks and caches?

The files that you have control over are located in the Documents, Downloads, Pictures, Music and Movies folders.  You can use this free app, GrandPerspective, to find the largest files on your drive so you can determine if they can be deleted or moved to an external HD for storage.

Note: you can empty the Downloads folder after the apps and/or updates that were downloaded have been installed or applied.  Some users have found a couple of Gigabytes of files in their Downloads folder which are no longer needed. 

Also, if you use Time Machine, launch Disk Utility and check for local snapshots in the boot container. This screenshot shows how:

You can clear your Mac's caches by doing a restart in the Safe Mode. Hold down the Shift key on restart. The startup process may take several minutes while the operating system clears its caches and does some repairs on itself. Then restart normally. What "junk" do you wish to clear? That is done by moving the files to the Trash and emptying it.