How can I see what a part is, once it's placed?

[KerbinObserver]

This seems like the simplest thing in the world, but for the life of me I can't figure out how to do it. How can I see the name of a part that's already been placed on a ship? Seems like super basic functionality that you'd expect in a mouseover tooltip, or something along those lines....

[CalculusWarrior]

Do you mean in the Vehicle Assembly Building or in-flight? You can't see a tooltip in the VAB when placing parts, but if you go into the actiongroups menu, then left-clicking on the part brings up a context menu including the name.

In-flight, simply right-click. If you can activate some sort of function for that part (e.g.: raise lander legs) then a tooltip should pop up.

[tommygunyeah]

Also,

If you're sorting stages, just hover on the icons and it will highlight that piece.