Update getting_started-public.md

Author: TimGoTheCreator

docs/getting_started-public.md

@@ -2,7 +2,7 @@
 
 NEXT is an N-Body gravity code for astrophysics and such. 
 
-## What does that mean?
+## What is Code / Astrophysics?
 
 Its a Computer program made in the low-level programming language C++ designed for running on workstations
 or supercomputers that simulates forces between objects called **"Newtonian Gravity"**
@@ -13,3 +13,21 @@ The term "N-Body" simply means **"multiple"** or **"many"** bodies, N could stan
 **"Body"** refers to such object in the simulation, it could be a star, a planet, or just particles.
 
 **So, an "N-Body" simulation is just a way of calculating how "N" objects move under gravity when they all pull in at eachother in the same time.**
+
+## Whats the purpose of NEXT?
+
+NEXT was made as an new simulation code written from **scratch**, to simulate interaction of bodies
+in short periods of compute time.
+
+## How is it efficient?
+
+The challenge is: if you have millions of stars, calculating the pull of each other on every one takes forever
+with the basic formula.
+
+The trick: **Barnes-Hut** instead of looking at each particle one-by-one NEXT scans the simulation and divides particles into groups
+and starts to treat them as "big stars".
+
+NEXT, however doesnt use basic Barnes-Hut; it uses **Barnes-Hut With High Ordering Multipoles**, instead of treating it like a "big star", it adds extra detail using a **dipole, quadrupole, and higher terms** into the calculation, adding shape and spread
+preserving accuracy of the engine (usually **5-7 times more stable**).
+
+That means that NEXT can simulate thousands (if not millions) particles at once interacting, while still being fast!