Kynou(?) wa nihongo o benkyoushimasu.

Kyou(= today) wa nihongo o(wo) benkyou shimasu(= present tense).

Kinou(= yesterday) nihongo o(wo) benkyou shimashita(=  past tense).

Demo watashi wa nihongo ga jyoso jouzu / jozu ja arimasen. Kanji wa taihen desu yo =[