Short Answer:
This is when the blister opens up and drains.
Long Answer:
Weeping is the most contagious and painful stage of an oral herpes outbreak. The blisters break open, releasing virus-filled fluid and revealing a raw ulcerated area. This stage lasts one day.

Short Answer:
From skin to skin contact.
Long Answer:
If a person has an active cold sore on their lip the herpes virus particles can be transferred to any part of the body that is kissed, including the mouth, face or the genitals. Keeping this in mind, it is very important to avoid kissing and oral sex during an active bout of cold sores.
It should also be made aware that the virus is considered to be contagious from the very first sign of an outbreak (including the tingling, itching stage) until the area is completely healed again. The cold sore virus can also spread at times when there are no visible symptoms due to what is known as Herpes Viral Shedding.
Herpes is most likely to be spread from the time these first symptoms are noticed until the area is all the way healed and the skin looks normal again. Contact with the infected area (including oral sex, kissing and touch) is very dangerous during this time.
It is also possible to transmit virus particles to another person through average objects such as a drinking glass, eating utensil, lip stick, lip gloss, toothbrush, a wash cloth, etc.

Short Answer:
Be very careful and hygienic.
Long Answer:
Avoid coming into contact with infected body fluids, such as kissing an infected person.
Don’t share eating utensils, drinking cups, or other items that a person with a cold sore may have used.

Short Answer:
One or two weeks, maybe more.
Long Answer:
While there is no set length of time, cold sores can last up to 2 weeks. If you can start treating it very early in the beginning you may be able to reduce the length of time significantly. In many cases it can be only 3-5 days in duration. The key is treating it as soon as you notice something is not right such as tingling or swelling.