The IELTS speaking test come in three parts.

Part 1: Introductions
Part 2: Topic
Part 3: Expansion

The introduction generally has 10-12 questions on a simple personal subject.
The second part consists of the student being given a card with a question and a minute to prepare a two minute talk.
The final part involves approximately 5 follow-up questions on the same topic as part 2.

The total speaking test lasts 10-15 minutes.

Note: Before part 1 the examiner will ask to see the student’s ID.

How the scoring works

The examiner marks 4 key areas:

fluency and coherence
lexical resource
grammatical range and accuracy

Each area is given a grade (0-9). The grades are then added together and divided by 4, giving the final speaking grade.

What the examiner is looking for

Fluency and coherence: Does the speaker speak without pauses and in clear sentences?
Pronunciation: Is it easy to understand what the speaker is saying? Are the words pronounced correctly?
Lexical Resource: Can the speaker vary his/her language? Can he/she avoid repeating the same words?
Grammatical Range and Accuracy: Is the syntax and grammar correct? Does the speaker show the ability to shift between tenses?

Each of the 4 areas is marked equally. Fluency and clarity, however, are arguably the most important aspects: it is supposed to be a natural conversation.

Students should note that using lots of long complicated words is not the point; most native speakers do not use overly complicated.  language.