The relative adverb is used to join sentences or clauses. The formal structure of preposition is replaced by the relative adverbs. The relative adverbs are where when and why. A relative adverb is an adverb that introduces an adjective clause.  Each adverb has its own role like where is an adverb of place, when is an adverb of time, why is an adverb of reason.

    To start a description for a noun the relative adverbs are used. This kind of description is called an adjective clause. Some of the example of relative adverb is stated below:
The place were we visited last day is still vacant. In this example seat is the noun and where is the relative adverb . The adjective clause identifying the seat is shaded.

I can remember a time when I could eat four pizzas. In this case, time is noun and the relative adverb is when.

We do not know the reason why she left our organization. In this example, the relative adverb is why.

Relative adverbs introduce relative clauses. The main reason to use relative adverb is that it joins two portions of a sentence together. They are used to join nouns and pronouns to the relative clause.

If it is possible to identify the relative clause then in that case it will be easy to identify the relative adverbs. The relative adverbs come directly before the relative clause. Relative clauses contain both subject and a verb. The relative clause begins with either a pronoun or an adverb. Beyond that, the main function of relative adverb is that they provide more information about the noun and the subject of the sentence. Some more examples are given to understand how the relative adverbs work

The 1800 were a time when men ruled and women obeyed

In this sentence the  subject is 1800. What about them? it is for the relative adverb when that we know more about this era.
So now it can be understood that when where and why are the most  general type of relative adverb . the words like whenever and wherever can also work as relative adverbs.to get an advance understanding of the use of relative adverbs the three main relative adverbs are required to be explained in more details:


When

First it is essential to understand what at the word when means. The word when allows to understand the time in which an action took place in a less formal manner.
Gone are the days when I could eat more junk foods.

Where

The next word is where. The word where allows to understand the location of the subject of the sentence in a less formal manner.
We seat on the table where we could see the view
This the tea shop where we could find the best cup of tea
This the house where they took their photos

Why

The word why provide more reason for some thing take place .
I have no idea why she called.