I have four cats.

• 四匹(よんひき) four (cats) [The 匹(ひき) looks like a 四(よん) but with a missing side. This 匹(ひき) is a counter for small animals like cats. Japanese has many counters, but English has a few too. For example: a cup of coffee]
• の (marker showing relationship and possession: 4 cats)
• 猫(ねこ) cat
• を (direct object marker)
• 飼(か)っています having (a pet); owning [The verb for owning/having pets is 飼(か)う not to be confused with the verb “to buy” which is 買(か)う.]

This room has four chairs.

• この this
• 部屋(へや) room; space [が indicates the subject in the sentence]
• には at; in [に indicates location; は makes it the topic of the sentence]
• 椅子(いす) chair
• が [subject marker]
• 四(よっ)つ four things [つ is a counter for general objects]
• あります there are; exist (polite) [This is the polite form of ある (to be; to exist)]

Cherry blossoms are very beautiful in April.

• 四月(しがつ) April [四 (four) 四月 (fourth month)]
• は as for [topic marker]
• 桜(さくら) cherry blossoms
• が [subject marker]
• とても very
• きれいです beautiful; clean (polite) [です makes the sentence polite]

My dog is four.

• 私(わたし)の my [の indicates possession]
• 犬(いぬ) dog
• は as for [topic marker]
• 四歳(よんさい) four years old [歳 is the counter for years of age]
• です is (polite)

Four people ate the pizza.

• 四人(よんにん) four people [人 is the counter for people]
• で by; with [indicates means or method]
• ピザ pizza
• を [direct object marker]
• 食(た)べました ate (past, polite) [past tense of 食(た)べます]