The categories that form the bold rows refer to the type of articulation. Stops are sounds that are maintained for a very short amount of time. You can't stretch no matter how hard you try. On the other hand, Fricatives can persists for forever. Sometimes you can merge stops and fricatives to get Affricates , which starts as a stop and turns into a fricative.
Nasals are, well, nasal.
They make your sinus vibrates. I have no idea why Liquids are called liquids. In other words, they are non-syllabic vowels. Even though they look like English, don't be tempted to pronounce the symbols as if they were English letters. Unrounded vs rounded .