I have never used an airlock before so don't know exactly what to expect.

The one I have has 3 plastic bubbles side by side

oo
oo
oo

The rest is in a kind of sideways 'S' connecting everything together (I
assume you all know EXACTLY what I mean...)

Anyway, how much water am I supposed to fill this with? Also, how violently
are the bubbles supposed to escape? There are a few tiny bubbles in the
water which weren't there previously!

The yeast is active and bubbles have appeared on the surface so I know that
everything is working (at least I assume it is!) Having released any build
up of C02, I know I will probably have to wait longer before it tries to
escape again, just would like to know at what rate!!

Thanks,
Simon