A big chunk of carbon atoms is just a boring frame. The "Functional Groups" are the specific clusters of atoms that actually do things. They give the molecule its personality:
Your DNA, your muscles, and the scent of a flower are all just organic molecules interacting based on their shapes. Summary of Basics Carbon is the backbone and always makes 4 bonds. Organic Chemistry for DUMMIES
Carbon MUST have four lines (bonds) connected to it. If it has three, it’s unhappy; if it has five, it’s impossible. A big chunk of carbon atoms is just a boring frame