Many jobs and some studentships start with a probationary period. It means that the institution is only guaranteeing to fund you for this period. If they do not think you have reached the required standard at the end of the probationary period then they can kick you off the course. A probationary period can be anything from 3 months to a year.
You shouldn't get too concerned about this. The institution has nothing to gain by losing you at the end of your probationary period and will only ask you to go if your really not up to scratch.