Yeah , Here I can explain you  in much simple ways .
Suppose here we have only one track to run a train ( btc ) but if we want run two trains than it is usual that we can't because at one track only one can run , so it would be more better to split the track into two , so that two trains ( btc and BTU new coin ) can run with the single foundation track .
I hope you understand with my this example .
Now another thing will come with this that is the improvement , The size of the block of the blockchain network will be increase so that unlimited numbers of the people can transfer Thier Bitcoin with low fee .
In this way in simple form we can say that the network and technology of the Bitcoin is going to upgrade , so that it can be use by the whole world without stopping the network and without facing any problems with fast speed .