These are sentences built from just one major clause. These have one main verb attached to the subject. The subject can be one word or a phrase.
Example 1 - Spiders spin webs.
Example 2 - The shaggy-haired Siberian Wolfhound sat outside.
A compound sentence joins more than one major clause with a conjunction (such as ‘and’, ‘but’, ‘or’).
It was raining and Sher had forgotten his coat.
Sophie had seen a parrot before but she had never seen an owl.
Zeb could go to school or he could go to the library.
A complex sentence includes a major clause and at least one subordinate clause. The term ‘complex’ here can be confusing. It does not mean the same as complicated. In fact some ‘complex’ sentences are very short and simple in meaning, eg ‘The cat mewed, until it was let in.’, whereas a simple sentence can be long and complicated in appearance, eg ‘The wild, ferocious Siberian Wolfhound from London’s Regent Park zoo escaped six weeks ago.’
In the following examples, the clauses are in bold. Notice how the major clause works without the subordinate clause:
The girl, who had long blonde hair, stood at the window.
While he does his homework, Jack listens to the radio.