Gravitational waves are perturbations of the very spacetime. They carry information about very wild processes which happen in the universe. On Earth, we are able to detect gravitational waves which are generated by collision of black holes or neutron stars. LISA is a project consisting of a space interferometer which consists of three probes, which measure distance with each other. Each probe carries a test mass which shades from outer influences. So, if the test mass moves, therefore it detects a passing gravitational wave. Thanks to high sensitivity of LISA, we will be able to detect gravitational waves which appeared during the very big bank when the very spacetime was created.
This will ensure a better mankind within just a few years.