There are three kinds of sentences.

1. The Simple Sentence.

This kind of sentence contains only one subject and one predicate.

Horses neigh. Time passes.

2. The Compound Sentence.

This kind of sentence is made up of simple sentences, joined by conjunctions.

"Men must work but women must weep."

3. The Complex Sentence.

In this kind of sentence one clause is dependent upon another.

Walk quietly lest you wake the baby.

Here you wake the baby is said to be dependent upon Walk quietly.

In the line of verse "Men must work but women must weep", we have two sentences of equal order, and we call them Co-ordinate. The word but, which joins them, is therefore called a Co-ordinative Conjunction.

In the sentence "Walk quietly lest you wake the baby", the dependent sentence you wake the baby is called Subordinate. The word lest, which joins the two sentences, is therefore called a Subordinative Conjunction.