Housing Benefit is normally claimed by completing a claim form provided by your local council. This could be online or a paper form depending on which council you are applying to. You will need to check with them directly and can do so by using the “find your local council” service on the gov.uk website - this will contain a link to your council's website and you can find specific information about applying for Housing Benefit there.
When making a claim for Housing Benefit you will normally be asked to provide proof of your (and your partner's, if applicable) national insurance number, rent, identity, income, capital and savings. If you have other adults living with you, you may need to provide proof of their income as well. If you do not have a national insurance number, you may not be able to claim.
In order to prove your rent, a current tenancy agreement or rent change letter is normally acceptable. If you do not have these to hand, you can log on to Your Waterloo and download or print your proof of rent document(s) from there.