There's this quest called 'Clearing the Tomb' in the Forgotten Tomb but I have absolutely no idea what I'm supposed to do. I tried exploring it but it didn't work. Please help!

I gather you didnt read the description of it before you accepted it? What you need to do is move Sylesti nests out of the tomb. In order to do that, you need to explore it for longer than however you did. As you do so, youll come across the aforementioned nests multiple times. Every time you do, youll be presented with a window that, I believe, has multiple buttons with different options (I dont recall exactly how many ATM.). Each time, you need to press the one that reads Move nest or something like that. You have to do that six or more times (Again, I cant remember the exact number right now.). Once youve done it, youll have completed the quest.