When barristers are first "called to the Bar", they act as junior counsel. A junior counsel may have the letters BL after his/her name, which stand for "Barrister at Law". Junior counsel tend to do most of the paperwork in cases (drafting legal documents) and they represent clients mainly in the lower courts (the District Court and the Circuit Court).
After about 10 to 15 years of practising as a junior counsel, a barrister may decide to become a senior counsel. This is sometimes called "taking silk" because the senior counsel's gown was traditionally made of silk. A senior counsel may have the letters SC after his/her name.
Senior counsel are very experienced advocates who represent clients in the High Court and the Supreme Court. Usually, if a senior counsel is involved in a case, there will also be a junior counsel to assist.