Today I will cover the use of “koto ga dekimasu” which means “can do something”.

Can speak Japanese – Nihongo o hanasu koto ga dekimasu
Cannot speak Japanese – Nihongo wa hanasu koto ga dekimasen
Meaning : Hanasu (Speak)

The verb shall be the original form (third sound) and it has to be placed just before the “koto ga…”. In the example above “hanasu” (sa shi su se so).

Another Example
Q : Can you make Japanese food? – Nihon ryōri o tsukuru kota ga dekimasu ka?
A : Yes, I can make Japanese food – Hai, nihon ryōri o tsukuru koto ga dekimasu
A : No, I cannot make Japanese food – Iie, nihon ryōri wa tsukuru koto ga dekimasen
Meaning : Ryōri (Food), Tsukuru (Make)

It’s easy. Go on, practise it and you should be able to master the usage in a short time.