Struggling with 'Malayalam' script: Why does 'ka' change so much?

I’m an absolute beginner, and I keep bouncing between three different apps because they all teach the Malayalam script differently—some use transliteration, some start with the alphabet, and others just use phrases. I find the conjunct consonants especially confusing. Is it better to just drop the apps and focus on hand-writing the script, or is there a systematic way to learn these character combinations without getting overwhelmed?