Semantics: This refers to the meaning of words and sentences. It's like the instruction manual in your toolbox that tells you what each tool does.
Phonology: This is the study of how sounds function in particular languages. It's like understanding which tool makes what sound when used correctly.
Morphology: This is the study of the structure of words. It's similar to knowing how each tool in your toolbox can be broken down into smaller parts (like removing a drill bit from a drill).