why should we create absract class and normal class.

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C#

hi,I have query when i should use abstract class,what is the use of abstract class over normal class.since Can do same thing with the normal class as well so why i should go for abstrct class,why we create abstact method.
eg

abstract class ABC
{
void myfunc()
{
console.write("hello");

}
abstract void abstfunc();

}
class b: a
{
override void abstfunc(){
console.write("override");}
}
main()
{
class b=new b();
b.abstfunc();
}

the same thing can be done with normal class as well also normal class can be instaintiated.so why we go for abstract class.

class ABC
{
void myfunc()
{
console.write("hello");

}
void virtual abstfunc(){
}

}
class b: a
{
override void abstfunc(){
console.write("override");}
}
main()
{
class b=new b();
b.abstfunc();
}

same implemented i can do using normal class as well just make a virtual function and overvide it.also having a default function myfunction,also i can make object of it.so why i shall go for abstract class.what are the benefit of abstract class and abstract method.
what is the use of this abstract method i can make a virtual function as well.