1.
If you ~ a topic when you are speaking, you start talking about it.
We got on to the subject of relationships.
PHRASAL VERB: V P P n
2.
If you ~ someone, you contact them in order to ask them to do something or to give them some information. (mainly BRIT)
I got on to him and explained some of the things I had been thinking of.
PHRASAL VERB: V P P n