To start with go to blogger.com create an account, then you need to decide what your blog is going to be about a lot of people like to just blog about there day and things that are happening in there lives.
The next step is to go to the monetize tab and sign up with adsense  this will then place ads on your blog and when people come to your blog they may click on the ads which in turn will earn you money.
Now all you need to do is create some traffic so there are places you can advertise your blog such as...Facebook,Twitter all other online chat sites and other peoples blogs where you can ask if they wouldnt mind taking a quick look at your blog.
Once you have traffic you will find that money will start coming in to your account but please remember this is not a get rich quick scheme it will take some time and effort to get traffic coming to your blog but if you can achieve a good steady flow of people you could be looking at earning £100-£150 per month.