You as the client will describe what you see as the problem and how it affects you. The job of the therapist is to listen and understand and to explore with you the aspects of the problem that are not immediately obvious. The whole basis of the relationship is that the therapist, being outside the problem, has no agenda and will be endeavouring to understand you from an unbiased viewpoint.
Part of what makes us human is our need for a sense of 'connectedness' with others we are a social creature and it is in the quality of our connections and relationships with others that determines to a greater extent our emotional well being. Being truly heard and understood is a powerful experience; developing the skill to hear us more fully, another significant aspect of what makes for effective and therapeutic growth.
Therapy sessions are normally once weekly. It seems that generally this is the most effective frequency as it gives time for the understandings and insights from each session to sink in and make sense whilst keeping up the momentum of change.
Most people will avoid this question for good reason. There are so many variables, however, a few rules of thumb may help so long as they are viewed as such. Most Employee Assistant programs normally work to a 6-session model. In my experience, if the issue relates to something recent or is a new occurrence then some positive change and improvement is usually possible in that time frame indeed I would expect to see at least some change within that time even with longer-term clients.
If the issue is lifelong a persistent feeling of being worthless for example then it is going to take longer not least because the longer you have spent telling yourself (or being told by those around you that you are useless, the longer it takes to undo that programming. Working in blocks of say 10 weeks you might expect perhaps a year of work. The best way is to try a bit getting some change achieved and deciding if you want to build on that initial success, working in stages.