I want to upload multiple images into plone site. Do Plone have the default functionalty to do this or should I install some add-on
this is built-in if you're using Plone 5.
for Plone 4 there are some add-ons that offer that possibility:
I am using plone 5. How can I upload images in bulk?
Click on the Contents link on the Edit bar, to view the folder contents
There will be an 'Upload' link at the top of the folder contents display that will bring up a pop-up where you either browse to the files you want to upload or drag-and-drop them onto the pop-up.