We can computer languages outside also so what is difference between that and joining a computer science engineering

Look, the classes for computer Science teach you a particular course, might teach you in detail too, but they don't have a 4 years courses where they teach you everything about the field of computer science including the sub fields so that you understand which subfield of specification you're interested in. So if you have it fixed in mind that you want to specialise in say Web Development, you can join an advanced web development class, but if you don't know, but have general interest in computers and coding, you take computer Engineering. All the best!