Well, go through it once more if you can, and try to answer to yourself why do people use algorithms, do not worry about exact algorithm, just that one question why do we even try to find algorithm. What happens when someone finds a better algorithm. Why do we even invent more complex data structures? Life is already hard so why to invent more complex algorithm. Is it only to test students in exams like GATE or does it have any real life implications. How do we even decide which one is the better algorithm among given two algorithms. Then go on to ask what does complexity mean, does O(lg n) mean it always takes lg n time, or sometimes takes lg n time?
What is best case or worst case algorithm?
Whenever we study algorithm we try to find out what all cases will slow our algorithm the most, thats called worst test case. Similarly what all situation will cause our algorithm to finish fast, those are best test cases.
Also get some real feel by writing code for some of the algorithm - write bubble sort, run it on a million randomly generated numbers, and just wait for it to finish. Then write quicksort and run it on a million random numbers and just wait for it to finish. Then write a $O(n!)$ to sort random 10 and 20 numbers. See the difference, feel the need for a better algorithm. And then you will really understand why would one even ask for "Worst algorithm". Since the worst algorithm has no limits, I can always write a worst algorithm by just putting while(true); before running any algorithm. No one asks for worse algorithm, that is against the whole point of having algorithm.