Analysis of a complex sentence involves the following steps:

1) Find out the principal or main clause.

2) Find out the subordinate clause or clauses

3) Classify each subordinate clause as a noun clause, an adjective clause or an adverb clause.

4) Show how each subordinate clause is related to the main clause.

Study carefully the following examples:

When the rain stopped, we set out for the next town, where we had planned to spend the night.

Principal clause: We set out for the next town

Subordinate clause 1: when the rain stopped

Subordinate clause 2: where we had planned to spend the night

Here the first subordinate clause ‘when the rain stopped’ is an adverb clause of time modifying the verb set out. The second subordinate clause ‘where we had planned to spend the night’ is an adjective clause modifying the noun town.

Now consider the following sentence

I know the man who said that this would happen.

Principal clause: I know the man.

Subordinate clause 1: who said

Subordinate clause 2: that this would happen

Here the first subordinate clause ‘who said’ is an adjective clause modifying the noun man. The second subordinate clause ‘that this would happen’ is a noun clause acting as the object of the verb said.

Another example is given below:

I think that he didn’t receive the letter which you sent him.

Principal clause: I think

Subordinate clause 1: that he didn’t receive the letter (Noun clause, object of the verb think)

Subordinate clause 2: which you sent him (Adjective clause modifying the noun letter)