What is the use of option FILL and BLEND in generative shape design in catia v5
2 Answers

Fill does what it says on the tin, if you have a surface with a hole through it for example, selecting the continuous boundary will fill the surface, with blend, you can connect 2 surfaces together some distance apart, I try to explain this in the attached pics, word of warning though, neither are a particularly great way of controlling the surface, I prefer to control with sweeps and splines rather than blend, but sometimes useful.