Although Trump's tweet reads like gibberish it would appear that he was suggesting something that he was hinting at something which is kind of true.
Nasa are currently preparing missions to the Moon as potential experiments to learn more about the challenges of sending humans to Mars.
This was confirmed by Nasa administrator Jim Bridenstine and also in a segment featuring Nasa chief financial officer Jeff DeWitt on Fox Business, which Trump was more than likely watching and got confused.
As @POTUS said, @NASA is using the Moon to send humans to Mars! Right now, @MarsCuriosity and @NASAInSight are on M… https://t.co/Yue3YfzPqG