Salat Duha is Nafli Salah, which is not mandatory but strongly recommended to believers. its conducted lonely not in congregation.
Time of this Special prayer
The time for salatu Dhuha is three hours past after sun rise and last for two hours before time for Dhuhur Salah starts during midday. you can pray minimum of two and maximum of either Rakaat quietly without voice.
One Rakaat means: Standing and read surat Al-fatiha, Then bowing and read glorification, then stand and read glorification, then prostrate and read glorification, then sit and prostrate again, read glorification. that is end of one Rakaat. if you stand and do same practice again, that second Rakaat. in every rakaat you read the same.