Fingerspelling has been around a long time - one early reference to a fingerspelt British alphabet is as early as 1698.
But it's only a very small part of British Sign Language - essentially a means of representing written English with the hands.
SignPost's FingerSpeller only shows signs for individual letters of the alphabet. They are done slowly to help you learn. They're not linked together.
But fluent fingerspelling is very quick. Individual letters form a continuous stream, so the fingerspelling can look different until you're used to it.
Think of the difference between English written in block capitals or in joined-up handwriting.