Distribution and abundance of plants in a habitat

I have been asked to: Plan an investigation to find out the distribution and abundance of two named species of plant in a specific habitat and to determine if this is effected by the water content of the soil.

I dont really know what the question is asking me to do or even where to begin.
Please could you try to explain what it is asking me to do - I can do the research myself, I just need to know what exactly is being requested.

Thank you so much!