General Training & Academic
There are two main IELTS test formats to choose from. The one you choose will depend on your reasons for taking the test. For example, if you are taking the test in order to take up a job offer in an English-speaking country it may be most appropriate for you to sit the General Training version of the exam. On the other hand, if you are taking the test to fulfill the requirements of a conditional offer to study at a university, then the Academic version would most likely be the one to choose. The format for these two versions is very similar. Only the Reading and Writing test differ – see here for more details.
IELTS for UKVI
In addition to the distinction between General Training and Academic versions of the exam, there is a further test category which may be applicable to you: IELTS for UKVI. The format of this test is exactly the same as the General Training and Academic test – the main difference is that the speaking test is video recorded (in addition to the standard audio recording). You are required to register for this if you are taking the test for UK immigration purposes.
IELTS Life Skills.
There is a third test offered by the IELTS consortium. This is IELTS Life Skills. It is used by UK Visas and Immigration for specific purposes, follows a different format to the two main exams, and is not covered in any detail on this site.
Double check before registering
In all circumstances, you should check with the institution, company or agency that you are taking the test for. They will be able to tell you which test format you should register for.
Paper or Computer
The final thing to consider is whether you wish to sit the paper-based version of the test or the computer-delivered version. Both options are available whether you are taking the General Training or Academic exam. So the choice is entirely yours.
The format of the paper and computerised versions is exactly the same. The results for the computer-delivered test are available more quickly, around 5-7 days, as opposed to the 13 days of the paper-based test. If this is important to you, then perhaps the computerised version is the one to go for. Bear in mind, though, that if your typing skills are not good, you might want to opt for the traditional format.