The first session
The first session is a chance for you and the therapist to establish the key issues that are causing you concern, how they affect you, and what is stopping you from moving on. It is important to establish what you need in therapy and where you would like to get to.
The therapist might ask you about how your past affects your current difficulties, what is perpetuating your distress, and what brings you into therapy now. They will also be aware of the 'therapeutic relationship' that is forming between you both and ways of working with this to optimise therapy.
If at the end of the first session you feel that you could work together, you can ask to arrange future meetings there and then. If you want a bit of time to think about it, the therapist will be fine with that. There should be no obligation for you to start therapy until you are ready.
If you do agree to meet again, you will need to agree on how to work together. The length of therapy will vary depending on your situation and needs. My approach is to arrange sessions for an agreed period and then have a review.
Once the time and location is agreed, then those sessions will be yours. Regularity and continuity are are useful in therapy as they give structure to the process. It is easier to be open to new experiences once a regular rhythm has got going.