How do colds form in a body?

i have a cold and i wondering why and how i got it. i have been sick for 2 days

Short answer:
Virus enters the body (usually through nose, mouth or broken skin). Body does not recognize it as "self" and attacks it. It keeps attacking it until virus is eliminated. Fever, runny nose, coughing and sneezing are not caused by virus but by your body trying to expel it out of you.
Long answer:
Virus is a strand of DNA surrounded by a membrane. It cannot replicate unless it finds a host cell. When it enters your body it attaches to your body cell and forces it to replicate itself along with included viral DNA. Since cell's DNA changes body no longer recognizes it as "self" and mounts an attack. First, non-specific defense such as fever and mucus in nasal and oral cavities. Several cells release hormones to aid in combat, e.g. mast cells release histamine to increase inflammation. Thermostat in hypothalamus is reset to cause fever. Several days later cells capable of specific immune functions activate. Infected cell try to prevent nearby cells from getting infected by releasing inferons. Infected cell presents a fragment of virus along with MHC-I complex to a T cell (CD-8) and Tc cell activates defense with costimulation (IL-2) by Th cell (CD-4). It releases defensive proteins such as perforin to kill infected cell.
Body remembers a signature of specific virus to combat it better during next infection. Problem with viruses is mutation. Usually virus you get infected next year is not the same virus you just battles so the whole process starts again.

The typical cold virus takes about 7 days to incubate, and then it takes another 2 days for your body to mount the counter-attack (which is what makes you feel sick). So if you've been sick for two days, then you actually were infected about 11 days ago. Probably got it from a phone, keyboard, door knob, any number of places.

the cold virus enters your body through your nose, your mouth, or any holes in you skin,
the cold virus os constantly changing shape, so your white blood cells cant attack it to keep it at bay,
the virus then multiples latching on to you red blood cells,
which then affect your organs,
eventually the white blood cells(love those guys)
will produce the right antibody's combat that cold virus,
you can get stuff to help out your white cells combat, but im not sure how they work,
lol
hope that helped