Income tax on rental income

Tax Planning and Financial

I think I am a bit naive about renting out my property. Last year I moved away with my girlfriend as she had found a job in London and I moved to be with her. I started renting out my house, and am currently living and renting a flat in London. I have gone through a letting agent to rent my house out and in my innocence I believed I was doing everything properly. However, it has just occurred to me about income tax from property rental, amongst other things. My questions are as follows, and I would be grateful for any help and advice.

1) The rent paid by my tenants is not more than the cost of the mortgage each month ie I make a loss renting out my house while I am living elsewhere. Do I need to declare and/or pay tax on this? I don't even know the first thing about any of this I realise. If so, how do I go about it? The directgov website is a bit confusing to me. I have heard something about private landlords asking for more tax relief(?), and I am wondering if this would even apply to me.

2) Is there anything else I may not be doing correctly or legally? I have all the safety certificates etc and I believe that my letting agent has done everything properly. It is a case of "I don't know what I don't know"!

Many thanks for your help