1) I know this may be hard for you. However, where to stick a comma or a period is considered grammar. Knowing the actual meaning of a word is entirely different.
2) Walking and chewing gum at the same time are two different actions.
3) I suppose if you have trouble performing 2. It is a bit unreasonable to expect you to understand 1.
Grammar
noun
- the whole system and structure of a language or of languages in general, usually taken as consisting of syntax and morphology (including inflections) and sometimes also phonology and semantics.
Definition
noun
- 1.
a statement of the exact meaning of a word, especially in a dictionary.