Answer:
In the beginning it may seem very complicated but as you start to understand the rules you won't even need the rulebook anymore.
The basics are fairly simple. Do not be frightened off by the size of the rulebook, the rules could be summarized into about 20-30 pages.
The game revolves around turns which consist of phases. Each player has a turn and carries out all of their phases before their opponent's turn.
The phases are:-
Movement
Magic
Shooting
Close Combat
Each player can select a number of troops up to an agreed points value. The troops are called units and most can be of variable sizes (eg 20 models) and some can be equipped with a variety of weaponry and armour for a predetermined pts cost.
All units have a profile:-
M = Movement
Ws = Weapon Skill
Bs = Ballistic Skill
S= Strength
T = Toughness
W = Wounds
I = Initiative
A = Attacks
Ld = Leadership
Most of the above are given a number from 1-10. The higher the number the better the unit.
Unit stats are compared between opposing units who come into combat or fire upon each other or use magic to see what damage they do to their enemy.
That in a nutshell is it !
It can get a lot more involved during a game but the basics are pretty straight forward and easy to pick up.