A contract is a legally binding agreement. Do not sign any contract unless you (and all your housemates) are completely confident that it’s fair and reasonable and that you can meet its terms.
It’s well worth checking with University of London Housing Services or the Students’ Union UCL Rights and Advice Centre before you sign any contract. These legal advice services are free to UCL students. Their friendly advisors can explain any legal terminology to you, as well as help ensure that you have the right kind of contract with no ‘dodgy’ clauses. Here, James from ULHS gives you some basic advice about renting in the private sector and ensuring you have a contract you can trust.