Carbon MUST have four lines (bonds) connected to it. If it has three, it’s unhappy; if it has five, it’s impossible.
These are "polymers"—massive, repeating chains of carbon.
Chemists are lazy, so they don’t like drawing every single letter. They use : Organic Chemistry for DUMMIES
Carbon usually hangs out with Hydrogen (1 bond), Oxygen (2 bonds), and Nitrogen (3 bonds). You can remember this using the acronym HONC (1, 2, 3, 4 bonds respectively). 2. Drawing the Molecules (The Secret Code)