The easiest and cheapest way to travel around London is with an Oyster Card.
Oyster is an electronic ticket that you can either top up in the style of Pay-As-You-Go phones or pay for travelcards that last for one week, one month or one year, depending on how long you pay for. The price also depends upon how many transport zones you go through.
To get a travelcard, you must first register your card online and validate it at a ticket office at one of the main stations on the Underground.
As a student you can apply for a Student Oyster Card which offers travel at discounted rates (30% off fares) for the length of your course. You need your student ID card, your course start and end dates, a digital photo of yourself to upload, and a £10 payment fee. TFL confirms that you are a student with the University and decides the length of time that the card will be issued for.