Not a driver, but from what I know, the levers are moved from the FLEX or TO/GA detentes to the CLB detentes to reduce to CLB power. You turn on either AP1 or AP2, then the bus flies itself for the climb, no intervention needed to maintain AoA. As for NAV mode- I believe it engages and will make the FD's move to follow the path above a certain altitude- but I'll let a bus driver tell you more.