Question

what is the difference between special relativity theory and general relativity theory

Answer 1

General Relativity is, quite simply, needed to explain gravity.

Special Relativity is the special case of GR, when the metric is flat — which means no gravity.

You need General Relativity when the metric gets all curvy, and when things start to experience gravitation.

Speaking from a practical point of view, the main difference is simply that GR is far harder to work with than SR.

In SR you can get away with knowing surprisingly little mathematics — this is simply not so with GR — the difference in required knowledge between the two is phenomenal. You cannot try and study GR without knowing tensor analysis — whereas for Special Relativity, you can get a long way before running into that (most people encounter it in electromagnetism, which is advanced special relativity)

Physically speaking, the main (well, the only) difference is gravity.

From the point of view of learning it — GR is much, much, much harder to learn and to do mathematics with.

The compromise is that, though harder, GR produces a lot of really cool results!