1. Complex sentences

2. What do we know so far?
Last week we learnt that sentence are made up of:
Words
barked
dog
big
And that words form single pieces of information called phrases:
A subject or noun phrase
and a verb phrase
barked
The big dog
Together these small pieces of information come together to provide a bit more detail in the form of a clause. A clause contains at least two phrases; a subject and verb phrase.
the big dog barked
Then we just need to add the punctuation and a capital letter, and we have a simple sentence.:
The big dog barked.

3. When I arrived the big dog barked.
Complex sentences
A simple sentence has just one clause that contains a noun and a verb; it puts a across one simple idea.
A complex sentence is used when you want to put across more detailed ideas. It contains one main clause and one or more minor clauses that are linked to it.
When I arrived the big dog barked.
The big dog barked is the main or independent clause because it has a subject and a verb. It can stand on its own, making sense without any help.
When I arrived is the minor or dependent clause. It relies on the main clause to make sense.

4. More complex sentences
We can add more dependent clauses to make a more complex sentence:
When I arrived the big dog barked because it was lonely
We can even split the independent clause with a minor clause and still have a complex sentence:
When I arrived the big dog which was lonely barked.