To answer this question as simply as possible I look to my friend and brother Duncan Forbes of New Life Church Roehampton.
Jigsaw Pieces – Systematic Theology
Systematic Theology is looking at what all the Bible says about certain topics. Systematic Theology picks a theme and looks all over the Bible to see where it is mentioned. A jigsaw puzzle.
The Story – Biblical Theology
Biblical Theology picks a theme and follows it through the one big story of salvation history.
Footnote: This material is directly quoted from Duncan Forbes course The Urban Ministry Program. I would encourage folks to take a look and do the course. It is challenging and helpful and will aid you in your walk with Jesus.