To insert a object in the mission editor
press CTRL + mouse click on a place
then click&hold and drag him to the right position
if you want to make it move around (waypoints)
CTRL + click on the place where you want it to go
you can asign multiple waypoints so you can let it move anywhere you want.
notice: you have 2 ship category's in the Object list
Stationary ships : cant move but will open fire at any enemy plane that comes near
Ships: can move and will open fire at enemy planes that comes near.
hope this helps a bit
edit: I found a online tutorial about the first use of the mission editor
this helped me out a lot. and contains more info about the mission editor.
http://www.il2-fullmissionbuilder.com/first-mission.html