Hi there, I'm Purple and I'm largely inactive on the forums now but I am a furry. It took me years to call myself a furry because of all the misinformation and misconception I was told about them, but now that I know the real truth, I'm loudly, largely, and unapologetically a furry.
Furries are broadly defined as "a person who enjoys the concept or content of anthropomorphic animals." What that means, at its bare-bones, is a furry can be anyone who likes the concept of animals acting like humans. This can even be down to animated moves like The Fox and The Hound or The Lion King--because those animals are given human-like traits.
Most people's general idea of a furry is an animal from Zootopia--an animal on two legs, walking and talking, sometimes wearing clothes--and yes! Those are anthropomorphic (in the furry community, that word is abbreviated to "anthro") animals too! "Anthros" are animal characters that walk on two legs and are generally what furries are associated with.
The costumes, which are called fursuits, are indeed incredibly hot; many fursuiters (people who fursuit) install little fans in the heads of the suits and wear cooling clothing underneath to prevent them from overheating and getting sick. They often have people who go with them, called "handlers" who carry their things and encourage them to drink water to avoid dehydration heat sickness as well!
Furthermore, not every true furry has a fursuit. Fursuits are INCREDIBLY expensive (the fur for mine alone cost nearly $100, the foam is an incredible expense, the work is tedious, etc) and so many furries don't have fursuits and are active in other parts of the fandom, such as art or roleplaying.
Every rosebush has its thorns, and there have been people outed for very nasty things in the furry community. But, for the most part, the community is very accepting and friendly!
Furries aren't all bad or disgusting or cringey or anything like that. We're just a bunch of people who like animals, costumes, and fun. If you have any other questions, feel free to contact me--if I'm offline here, ask Crim, Bengal or Vul (is Vul still active? ...is Bengal even still active) if they can get a hold of me for you.
Thank you for your kind interest!