Theory test advice

There are 2 parts to the driving theory test: a 50 mark multiple choice section and a 75 mark hazard perception test. To pass you need at least 43 on the questions and 44 on the hazard perception test.
It's probably a good idea to buy either a book or a computer program to learn what you need to know.
Once you've done a few practice teats it isn't too hard. If you've done no driving yet, you might find the hazard perception quite hard. They play you a sat of clips from the drivers perspective, driving in different locations. You have to click your mouse when you see a developing hazard. The sooner you spot it the more points you get (max of 5 per hazard) most clips have 1 hazard in but 1 will have 2 hazards for you to spot.
the types of questions you can get on the first section include:
Identifying different signs (they can ask about the shapes of signs too)
Different types of pedestrian crossings
What to do around vulnerable road users
Things about insurance, MOTs, your driving licence
Information about using motorways
Safety margins (learn stopping distances in different weather conditions)
What to do if you are involved in an accident or attend the scene of an accident (including giving CPR and basic first aid)
Speed limits
Things to do with loading a vehicle e.g. the effect of a roof rack, suitable child restraints ect.
Driving in different road conditions (e.g. at night, in different weather conditions, when it's icy)
Safety in your own vehicle
Stuff like that. There are plenty of free online mock tests you can have a look at.