Combining Clauses

A simple sentence is made up of only one clause; therefore, if you compound multiple clauses you get a compound sentence

Coordinating conjunctions are used to form compound sentences, the coordination conjunctions are:

and: in terms of linking two facts together

and: in terms of evens happened in the order they are listed

and: a casual relationship

but and yet: second clause is contrary to the first

or: disjunction, the clauses are alternatives to each other

for: the second clause gives the reason for the first

nor: negative clause, makes the second clause mean "and not"

It is important not to confused coordinating conjunctions with sentence adverbs and to be sure comma use stays consistent with them. 

Ellipsis is when you eliminate some redundancy in a sentence by omitted "ellipted" material that would otherwise make the sentence repetitive.

Example:  The man left the bar and the woman left the bar.

or: The man and the woman left the bar.

If you remove enough information, sometimes the sentence is no longer compound but still contains a coordinating conjunction

She wrote a poem and she wrote a short story.

She wrote a poem and a short story. 

Subordination: the clauses do not share equal grammatical status. 

When the dog growled, everyone stepped out of his reach.