It seems there is still some confusion,
the main symptoms to look out for are a high temperature on the chest or back and/or a new continuous cough (a cough which lasts over an hour or 3+ coughing episodes in 24 hours)
A lot of people have very mild symptoms, much like the flu or a cold, and the exact symptoms can vary between people.
The severity in a normal, healthy, person will be governed by the viral load, this means basically howuch of the virus they get in their system.
I'm far from an expert but my understanding of this is as follows:
If one unit of the virus gets in to your system it will begin to multiply and your body will begin to work out how to fight it, after a period of time your body will work out how to kill it and proceed to do so.
By the time your body has worked out how to kill it that one unit of virus may have multiplied to 100 units.
However if you start with 10 units in your body then by the time your body has worked out to kill it there are 1000 units in your body and you are far, far more ill.
It is not the case that once you have caught the virus you have it and that is it, every time you pick up another dose from another infected person it increases your viral load.
This is why if you catch it you need to keep away from people, even other people who have caught it.