By support, I just mean that ideally your feet have been measured, running style analysed and your trainers have been properly fitted, by staff at a specialised running shop, rather than just buying the first pair of Asics you see in JJB.
LISS is Low Intensity Steady State, just running at the same steady, manageable pace for a decent length of time. It's better to do this for the first couple of weeks so that you have a decent fitness base before getting tanked into HIIT.