my first kpop group I listened to was SHINee, back in 2009 (with ring ding dong). But the group that made me fond of kpop is KARA. 
Mine was FT Island and then Super Junior!
I'm not sure about my first FTI song - maybe Girls Don't Know or After Love?
Super Junior it was Sorry, Sorry 
That would be DBSK.. Wayback 2008..
I got into K-Pop last year with BTS's "Dope"
The first kpop song i've heard was shinee's love like oxygen but the group that made me like kpop was EXO with Groul 
BIGBANG - Haru Haru
My first song was big bang's lies. I watched it around the time it came out because it came on the recommended tab when I opened youtube but I actually got into kpop in 2013 with SUJU's Mr. Simple.
Either Big Bang's Haru Haru or DBSK's Hug... I can't remember which was first! But then I took a long break from k-pop and got back into it last year with BTS's Boy in Luv :p
Wonder Girls - Nobody
DBSK was the first band I was introduced to and the first song I heard was Mirotic. I discovered BigBang, SHINee, and Super Junior shortly after but then took a long break from kpop but then got back into it recently. 
my first kpop song was either wonder girls' nobody, big bang's lies, or SNSD's Gee. Can't remember. But for sure the group and song that got me into kpop was Exo's Call Me Baby
bigbang
fantastic baaaaaaaaaaby