When to shift?

Hey guys. I am from Switzerland and I have a '68 Valiant 170 cui with three on the tree. (not running at the mom.):poke:

In Switzerland about 80% of the cars have manual transmission, so I know how to shift and the position of the gears...

BUT I never drove a car with less than 4 gears.
Now I just want to ask you (because I can't wait till I can drive it myself :p) when I need to switch the gear?

For example: With my 6-gear-transmission I switch from 2 to 3 with 30kmh (18 mph)

How is it with three on the tree?

Sorry about my orthographic mistakes:BangHead: