You already knew two Indonesian words
Orang is person. Hutan is forest. Put them together and you have the animal everyone can name in English: person of the forest.
Orang is one of the most useful words in the language and it is everywhere: orang Indonesia 'an Indonesian', orang tua 'parents', orang asing 'a foreigner'.
Two words for animal, and they are not swappable
Binatang is the everyday word and hewan is the formal one, but neither is free to move: each has settled into fixed expressions. A zoo is a kebun binatang, an animal garden. A vet is a dokter hewan. Swap them and you are understood, and you sound like a translation.
Point binatang at a person and it is an insult, which is worth knowing before you use it to be funny.
Kupu-kupu is not two butterflies
Doubling a noun in Indonesian usually makes it plural: buku 'book' gives buku-buku 'books'. Then you meet the animals and the rule stops working.
kupu-kupu butterfly
laba-laba spider
ubur-ubur jellyfish
kura-kura tortoise
These are not plurals. The doubling is part of the word, and taking it off leaves you with something that means nothing at all. One butterfly is kupu-kupu, and several are banyak kupu-kupu, because the number word does the counting whenever there is one.
Anak saves you a whole vocabulary list
English makes you learn kitten, puppy, calf, chick, foal, cub. Indonesian uses anak 'child' and stops:
anak kucing kitten
anak anjing puppy
anak sapi calf
anak ayam chick
The same shortcut runs through the meat on your plate. Daging is meat, so beef is daging sapi, meat-of-cow, and pork is daging babi. English borrowed a separate French word for each animal once it reached the table. Indonesian did not bother, and there is nothing to memorise.
Sea-dog, sea-horse, sea-star
Compounds put the main noun first and the describing word second, and the pattern runs and runs:
anjing laut sea dog, a seal
kuda laut sea horse, a seahorse
singa laut sea lion
bintang laut sea star, a starfish
Gender works the same way, by adding a word rather than changing one. Indonesian has no grammatical gender at all, so a rooster is an ayam jantan and a hen is an ayam betina. Jantan and betina are for animals; laki-laki and perempuan are for people, and putting those on a chicken lands exactly as you would expect.
The animals that will actually be in the room
Tigers and elephants are on the signs. This is the list that earns its place in your first month.
Nyamuk mosquito, and obat nyamuk the coil you burn against them. The compound names what the thing is aimed at, not who it treats, so cream for the bites is obat gatal, itch medicine, and a net is a kelambu.
Cicak is the small pale gecko that crosses your ceiling in silence and eats the mosquitoes, so leave it there. Tokek is the big one that shouts its own name at two in the morning. Dictionaries print cecak for the small one and nobody writes it that way.
Tikus covers rat and mouse with one word, kecoa is a cockroach, and semut is an ant. Those three turn up in the same conversation as a leaking tap, which is what the lesson on household problems is for.
The animals people throw at each other
Anjing is a dog. Shouted on its own it is a swearword with about the force of the strongest one in English, which is why Jakarta filed the edge off it into anjir and anjay. Inside a normal sentence the dog is just a dog. Monyet 'monkey' works the same way, and the monkeys at Uluwatu will take your sunglasses regardless.
Then there are the ones that are almost affectionate:
buaya darat land crocodile, a man who chases women
kambing hitam black goat, a scapegoat
kutu buku book louse, a bookworm
English arrived at the same picture for the last one and a different one for the other two, which is roughly how idiom works everywhere.
Where this goes next
Three of the questions above were grammar wearing an animal costume. The doubling rule is settled properly in the plurals lesson, and the meat words carry straight over to reading a menu.