A group of words that makes complete sense is called a Sentence.
1. When did you go to Germany?
2. The Alps are very beautiful.
3. How beautiful the cake looks!

A group of words that makes sense, but not complete sense, is called a phrase.
Very beautiful

A group of words that form part of a larger sentence, and contains a subject and predicate, is called a clause.
This is the salesman who came here yesterday.
‘Who came here yesterday’ is a phrase.

Sentences can be of four kinds:
1. Assertive or declarative which says or states something.
2. Interrogative which asks a question
3. Imperative which expresses a command, a request or an advice.
4. Exclamatory which shows strong feelings.