A key goal of cosmology is to understand the accelerated expansion of the Universe, believed to be driven by a force called Dark Energy. Mapping the distribution of galaxies throughout the Universe's lifetime can measure the expansion and help us understand the nature of Dark Energy. In the past decade, a new method called HI intensity mapping has emerged which uses the radio emission of gas to trace the galaxy distribution. With the support of the UKRI FLF fellowship, I will prepare the up-coming HI intensity mapping observations by the Square Kilometre Array, the largest radio observatory ever built, as well as analyse its recent pathfinder data. These new radio surveys will allow us to get unique insights into the evolution of our Universe, inaccessible to optical telescopes.