I always had a problem with who whom whose

Worse is a comparative, a word that compare between two stuffs.
Therefore, worse should be used to compare between two things, such as in the phrase, "My apple is worse than yours". You can also break the comparison to two sentences, as in, "Your apple is bad. However, my apple is worse." Always note that comparative words must oppose to something.
Worst is a superlative, a word that express the highest level of something.
Therefore, for worst, it is the highest level of 'badness' you can achieve. In a phrase, "My apple is the worst." That means the apple is the baddest compared to all there is.
Briefly, you can treat worse as 'lebih buruk' and worst as 'paling buruk'.
Subject to errors and correction.

bad        -  worse          - worst
(positive -  comparative - superlative)  in grammar terms

They are the different degrees of adjectives. Adjectives are words to describe a noun/thing.
The comparative is used to compare two things.
The superlative is used to compare three or more things.

Other examples:

good - better - best
happy - happier - happiest
beautiful - more beautiful - most beautiful