Question

how can you group several objects into a single object ? what are its advantages

Answer 1

We can group objects on the basis of their colour,shape,size,odour,taste etc
It's main advantage is it saves our time to find them later

Answer 2

If you want to group the objects, then you have to transform and move the objects in the group as the single unit then you can change properties.

For example, the line size and the color fill of the group as the whole and the individual objects in the group.