Learn the number system.Basically just the number of the notes of the scale of a particualr key you are playing in.. You'll find a lot of Rock,country,are built around a 1,4,5 pattern,or sight variations. 1,minor 3rd,4(Smoke on the Water)which would be G,B flat,and C,etc.. Country,especially modern country will sometimes add a 6th in the mix somewhere. Wouldn't worry about slash chords yet. Learn the basics and go from there.After a while you will here similar patterns,just played in a different place on the neck. Listen to any Steely Dan album for example of more complex chord structures. Aja' is highly recommended.