If you need to evaluate usability of your product, the first thing you will have to do is to develop a profile of your target audience.
Target audience profile is built on the basis of intersection of multiple goals being part of the projected or already existing functional attributes of the product. Such goals can be pursued by potential or current product users.
This will allow you to identify the groups of TA, who can achieve their goals through application of certain functional elements of the product.
Definition of each target audience group may include gender, age, education, income, past experience with your product or other similar products, etc.
Then, you will need to make a list of goals your product users are interested in and to describe the environment they find themselves in.
As a result, you model various scenarios of product application by concrete users in concrete contexts. Analysis of factors contexts arise from might add more items to the goal list thus expanding the target audience coverage.
User interaction with a product can be visually represented by the following diagram (according to ISO-9241):
Obviously, product usage by unspecified users or in unspecified contexts might result in failure to achieve goals sought by such users by means of the product, or in improper product operation.
As soon as the target audience profile has been built and user goals has been defined, you are to draw a list of usage scenarios, where each scenario is a sequence of actions (tasks) performed by users to achieve their specified objectives.
Now you are ready to start usability-test designed to gauge product usability comprising the following parameters: Effectiveness, Efficacy, and Satisfaction.
Users and Goals | Effectiveness | Efficiency | Satisfaction | Methods