An argumentative text is one that developes argumentation that is a thesis expressing the point of view of the writer or speaker, if the argumentation is oral.

To write an argumentative text the writer has to select the most important ideas, next he has to organise them and expand them.
The argumentation must be clear and sustained by qualitative and quantitative arguments and reasoning.
The writer has to compare the advantages and disadvantages of the topic.
The purpose of the argumentative text is to persuade, to convince others that the idea is credible.
It has to be structured into three paragraphs. The first one is the introduction where the writer introduces the subject of the discussion. Then a central body where he addresses a discussion about the topic developing his thesis and antithesis and discussing the relative causes and consequences, features or advantages and disadvantages. The last one is the conclusion where the writer gives a personal opinion and he presents the possible solution if the subject of discussion is a problem, bringing the discussion to an end.
An example of an argumentative text are textual analysis where students or the writer of the textual analysis has to analyse a text and he developes an argumentation about what the massage is resolving, to conclude about the literary choices the poet made.
An other example are oral argumentation that students listent to. Also an own opinion is an argumentative text.
The condition for an argumentative text to exist is that there is an argumentation or a point of view.

The writer can use different expressions to support his opinions like:
A further argument in favour of /against... is...
Another point in favour of/ against... is...
Bearing this in mind/ considering this, I think...
First of all...
I think...
If... then...
In my opinion...
It’s important/true/necessary to remember/to point out that...
It’s worth remembering that...
No doubt... however...
One advantage/disadvantage of... is...
One objection to this argument is...
Take for instance (to present an example)
The biggest advantage/disadvantage is...
This is not always the case...
To sum up/In conclusion I would say that...

Or he can use different logical connectives (to contrast thesis and antithesis) or adverbs (to persuade):
above all, additionally, also, as a consequence, as a result, as well, at least, besides that, certainly, clearly, despite, especially, even if, evidently, further more, however, in addition, indeed, in contrast, instead of, in particular, it would seem, like, moreover (used to add another point), naturally, obviously, of course, one might consider, on the other hand, otherwise, therefore, unless, whereas, while