There are two main categories of Tsundere: Harsh: (or Tsun): These Tsundere have tsuntsun as their default mood. It takes someone special to trigger their deredere side. The intensity of the tsuntsun can range from "I must glare and fight my way through life" to grumpy pessimism. It's about which part of the tsundere personality is the public face and which the hidden. If the Tsundere is The Rival, she is more likely to be Harsh. Helping a rival out is usually accompanied by a line like "Don't get me wrong, I'm not doing this for you."
Sweet (or Dere): These Tsundere have deredere as their default mood. They are sweet, kind and generous, but just happen to have a hidden violent side as well. In this case, temper is almost always triggered by someone or something else, usually a Love Interest. Either they have Belligerent Sexual Tension (A couple who will usually have a 'grumpy female' which can be only noticed from the couple which would later result to feelings being admitted,although persisting it being only a friendship), are an Accidental Pervert, or just have no idea how to handle feelings of love and attraction. it may also overlap with Violently Protective Girlfriend if her Love Interest is threatened or in danger.
Sweet types should not be confused with a Yandere. If a Sweet Tsundere were really convinced that their Love Interest didn't want them, they would revert back to the deredere side and probably enter an I Want My Beloved to Be Happy phase, while Yanderes are Not Good with Rejection at all and have been known to get downright murderous under such circumstances.
Above is a short (looped) clip which goes through the pronouncing of Tsundere. To be brief, the T in 'Tsundere' is not pronounced and is a silent T. Making the pronunciation, 'Sundere'
Male Tsundere's Edit
Specifically, male characters who have this trait can be still regarded as 'Tsundere' however can be known as: Oranyan, which ironically means the opposite to a Tsundere.