Firstly welcome to GoY, you will find all the answers you need right here.
If you are after a book there is no better resource than your local library. That and the fact it is free!
You will need to decide :- What you wish to grow (Flowers or veg?)
How you want to grow it (Organically verses not?)
and above all if I could only give one piece of advice that would be, enjoy it!
Good luck!

~if you want books to buy for yourself have a look on Amazon~alan Titchmarch and the RHS do good series for beginners~

The first thing I'd do is get rid of the paraffin heater. Paraffin is expensive, the heat cannot be controlled and produces fumes and water vapour, and is likely to run out of fuel in the middle of the night in a frost.
Get a really cheap fan heater with a 'frost setting' and use this and you will find it costs far less to run, with much greater efficiency.
Obviously electrical safety is vital, so if you simply plug it in on an extension cable, you MUST make sure it is completely disconnected before you do anything in the greenhouse which requires water.
What you do next depends on whether you want to use your greenhouse to raise flowers such as half hardy annuals, or vegetables. The greenhouse is the ideal place to start seeds for planting out later. But be aware that temperatures can soar in a small greenhouse on a sunny day and more seeds are lost by being 'cooked' than ever suffer from the cold. Shade your seed pans with fleece.
There are so many books available it's hard to recommend one in particular. Have a look on line first as there is a vast amount of information there without buying a book.

have a look at a book called the greenhouse expert at greenfingers .com it cost £9.00,get the opions of an expert.because all well intentioned advice on site will differ and confuse a biginer,we are after all hobby gardners, even though a lot have a life time experance,have the book to hand as it gives you step by step instructions,then in future you can discus and know what people are talking about.,I wont myself talk about pariffin heaters, although I have just bought another one,at nearly seven pounds for four leaters though it is dear,

I AGREE WITH BERTIEFOX, GET YOUR SELF A CHEAP ELECTRIC FAN HEATER,WITH FROST GUARD SETTING, ITS WHAT I USE AND ITS GREAT. ARGOS DO SOME GOOD ONES

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THIS IS THE ONE I HAVE

I have an RHS book called 'Propagation of Garden Plants'......at least I think that's what it's called.....I've been looking for the darn thing all day and it still hasn't turned up... :-S

The only reason I would choose paraffin would be if I could not lay electricity safely. On the other hand, you have the pariffin heater so you might as well use for this winter, at least.
I am sure that you want to get started as soon as possible so buy some seed or multi-purpose compost and some seeds annual plants and half hardy annuals (you will need the warmth for these). If you want to start some vegetables then get some early cabbage and some cauliflower on the go. This will all largely depend on where you live. In the north of Scotland I will not be sowing until the end of the month (Allah willing)!
Welcome to GoY and enjoy your greenhouse. You will get most of your experience by trial and error.

welcome to goy to shfiske

just like to add to what BH said only use your heater at night and when it is frosty, mine will last 19 hours continual burning on 4 lt so only use it to keep frost away otherwise it will be a dear do.