A Marketing Matrix is essentially a plot on a two-dimensional plane according to how well they meet customers’ key requirements.

You can do this by drawing two lines in the form of a cross. These two lines represent a continuum of bad to good performance for two benefits or attributes that are the most important in an industry.
For example, take computers. If the two most important things to customers are “performance” and “price” then, put the word “performance” at the top of, say, the vertical line and put the word “price” to the right of the horizontal line.

High performing computers would be plotted at the top of the vertical line, and low performing computers at the bottom of the vertical line.

Now, for each computer in the market you would plot where that computer fits on the performance line (compared to other computers) and on the price line.

One comment: A marketing matrix is essentially a perceptual map. You can read more about snake plots as a better way of doing this since a marketing matrix forces you to do this in 2 dimensions, and often more than two dimensions properly characterize a market.

Source : http://www.marketingprofs.com/

Before start think about marketing (4P), you must understand what is STP. Terms of STP include : market strategy; target markets; positioning; market segmentation and target markets; market segmentation and demographics
Segmentation
Segmentation : Identifying al segments for the product/service. Many of the resources listed in module 3 will be helpful to you when you develop segments. To be useful, segments should be:

Measurable
Accessible (can you reach them)
Profitable
Distinct from one another

The objective of segmentation is to find attractive markets. Strategies include

Break market into components
Regroup into market segments
Select which segment to target

Positioning.
Positioning is an essential component — and skill – in good marketing. Perceptual maps are used to determine the position of a product, firm, person, service or idea. Positioning maps, or perceptual maps can be simple, yet very effective marketing tools. One definition of Positioning Theory is: the science of perceptual strategy. It is based on a theory that strategy can only be planned in the mind of the consumer, not the marketplace*.

It is important to understand the levels of competition because positioning applies at all levels of competition. For example:

Product Level (e.g., Pepsi vs. Coke)
Category Level (e.g., Cola vs. Root beer)
Corporate Level (e.g., Pepsi Inc. vs. Coca Cola Company)
Industry Level (e.g., Beverage Industry vs. Snack food Industry)

Targeting.
What is target?. This is the real goal/objective in market that marketer want to reach.

As a simple questions are :
What percent of the population uses the product at all?
What percent uses your brand?
How does that compare to competing brands?
What is the demographic profile of the product category?
Which media reach the users of this category?