By this time the TOEFL can only be absolved as computer-based test (that means you don´t have to write anything on paper but you can write at least the essay with pen and paper if you prefer this - see below).
You should be able to use a computer now how to work with a mouse but if you made it to this page, this should be no problem for you. But if you feel uncomfortable working with a mouse you should train this. In other words, you will have some (time) disadvantages during the test!!
You can´t fail the TOEFL! You will get points for the different sections of the test (reading, listening, structure/writing and an essay) as well as an overall number of points at the end. Different institutions which require the TOEFL have an individual number of minimum points for their applications - you should find out about this before you take the test.
Every person that feels more or less comfortable in speaking, listening and reading English (books, films, conversations etc.) should have no problem to get good points. Have in mind there are different books and CD-Rom´s for the direct test preperation.
It is recommend reading English newspapers or magazines (i.e. you can get the TIME-Magazine at almost every place on the world - in some countries there are very cheap subscriptions for students!). This is very recommendable especially for the reading-part of the test.
You can begin to periodically watch english movies once or twice a week to practice for the listening part of the test (in your country you might be not very often have the opportunity to watch english movies on TV. So, you may also have the opportunity to download movies (illegally) from the internet but that´s your descision).