Hi folks.

I have just picked a crew with Lester, think it is for a jewellery store raid.
Anyway, the map doesn't give much away, so i'm not sure where i am supposed to be going/doing next.
I can see little green question marks on the map, but when I go there, nothing happens.
Lastly, how do I switch characters, or does the game automatically do it for me via story related?