Table index rebuild & index fragmentation

Hi Team,

Can anyone help me to understand below topics / questions :

Table index rebuild & index fragmentation both are same or different?

Is it recommend to do the index rebuild for bigger table like F0911 ?

If Yes, can we use JDE application for rebuild or using Database side ?

Any performance degradation after performing index rebuild ?

Any negative impact of doing index rebuild for Big table ?

Any negative impact or performance degradation of doing index fragmentation ?