Please practise in accordance with this Mahasatipatthana Sutta so that you can see why it is acknowledged as the most important Sutta that the Buddha taught.
Try to practise all the different sections from time to time as they are all useful, but in the beginning start with something simple such as being mindful while walking (see Iriyapatha Pabba), or the mindfulness of in and out breathing (see Anapana Pabba). Then as you practise these you will be able to practise the other sections contained within this Sutta and you will find that all the four satipatthanas can be practised concurrently.
A sutta should be read again and again as you will tend to forget its message. The message here in this Sutta is that you should be mindful of whatever is occurring in the body and mind, whether it be good or bad, and thus you will become aware that all conditioned phenomena are impermanent, unsatisfactory and not-self.
The original Pali text of this Sutta can be found in Mahavagga of the Digha Nikaya.