Number + 月
四月 (sìyuè) means "April," the fourth month of the year. Like all Chinese month names, it is formed by placing the number before 月 (month). Use 今年四月 for "this April" or 去年四月 for "last April."
四月的天气特别舒服,不冷不热。
sì yuè de tiānqì tèbié shūfu, bù lěng bú rè.
The weather in April is especially comfortable, neither cold nor hot.
我打算今年四月去日本看樱花。
wǒ dǎsuàn jīnnián sì yuè qù Rìběn kàn yīnghuā.
I plan to go to Japan to see the cherry blossoms this April.
她的生日在四月十五号。
tā de shēngrì zài sì yuè shíwǔ hào.
Her birthday is on April 15th.