I'm a Malaysian student who has a Tier 4 student VISA and if my visa expires on June 28, how long could I continue to stay there if I want to tourist to explore the place. Or I need to go back to Malaysia on 28 of June? Please help me out. Thanks!
Before your Tier 4 student visa expires, you will need to leave the UK. There are only a few visas which you can switch to from Tier 4, most notably Tier 2 (general), and the Standard Visit Visa you would need is not one of them. On the other hand, as a Malaysian, you are allowed to enter the UK visa free for the purposes of tourism. You would still need to leave the UK and reenter with this new purpose, however. You could accomplish this by, for example, taking a ferry to France and back.
However, be warned that border officers subject visitors who have recently resided in the the UK to extra scrutiny, and you will need to ensure you have good evidence that you will return to your home country afterwards, which in your case might be quite tricky since you will presumably be unemployed. If you do attempt to reenter the UK for a visit, make sure you have tied up all your loose ends from your studies (eg, returned house keys, and shipped belongings home). You might be better off waiting a year or so before attempting to enter the UK, unfortunately.