「歌う」 is a common way to write 「うたう」. We usually use 「歌う」 in our everyday life. In a more limited sense 「歌う」 is used for Western-style music and meanwhile 「唄う」 is used for traditional Japanese music like long epic songs, little ballads and folk songs. So you can use 「歌う」 for to sing, to chant or to recite but there's no equivalent English word for 「唄う」