its quite easy, its is telling u to play a Dm but the number is telling u have to play an extra note in that chord, to work out that note u just start at the tonic or root note of that chord in that case is like a D then u count up 7 notes in the d scale, and u add that note same with other notes like 6 9 13 etc, but with 7ths its a bit differnt when they say 7 they mean minor 7 so for the the chord D or D minor it would C but when it says major 7 that is the 7th note in the scale. When u found that note u just stick it in any where and just play it, But when i play i usaly through in like 2 and 4 (which can be called 9 and 11) in the chord to make a phater sound. I hope that helpfull if ur confused (u can be) give me a yell
