Paper 1 is a source-based 'skills' examination. In the space of 1 hour you have to answer 5 questions taking into consideration four sources. At least one of these sources will be visual. Perhaps the biggest challenge students face when taking paper 1 is managing time as there is a lot to do in only an hour.
The key thing to know, however, is that despite this nominally being a 'skills paper' and there seemingly being so much to do in an hour, it is in fact very easy to study for because the format of the questions is exactly the same every year. So all you need to do is practice each type of question and make sure you have a watch on your desk on the day.