I am going to buy an iPhone 5s 16GB. Now my query is whether any videos that I still store in my phone can later get transferred into my laptop? That way I can save spaces by not keeping unnecessary videos, images, etc.
Yes. This is very easily done. All you need to use is iPhoto. Plug the device in, and (if it hasn't already,) open iPhoto. Click your device in the left-hand side menu, and click "Import Photos" on the prompt. The photos & videos will now be imported.
At the end of this, there will be another prompt. Click "Delete Photos" and the photos & videos will be removed from your device.
One can use iPhoto.app or Image Capture.app or Apeture.app to download photos from your iPhone.
Image Capture.app is available for free on any Mac with as part of the system installation, while iPhoto.app (free) and Apeture.app (paid) are pieces of software available in the online App Store. iPhoto.app also comes bundled as part of a new Mac purchase, so most users have a copy installed on their machine.
Apple has instructions on importing from an iOS device to all of these pieces of software, as well as info for Windows computer users:
iOS: Import personal photos and videos from iOS devices to your computer
On iPhone, iPad, and iPod touch, you can capture photos and videos using the built-in camera or save images from apps, such as Safari and Mail, to your device. You can import this content from your device to your computer.
Mac Observer has some more info about using Image Capture.app which is also great for scanners and other cameras: