if i run command from Pl-sql command prompt for inserting multiple rows one by one without rewriting statement again & again we can use & operator, as shown in below figure.

if i used GUI method for same purpose, i have to use : operator,as shown in below figure

now my question is-> why we cant use & operator in GUI , if we used it gives error.
What you have encountered is a text replacmenet mechanism of SQLplus (and tools that implement the same extension).
You can turn it of with:
Or you can switch to a different character (the plus sign in this example):
The Oracle tool you’re using doesn’t implement the SQLplus extension as far as I know. But SQL Developer (a free GUI tool from Oracle) does.