You need to do all the objectives in all the levels of the first board. Some missions force you to redo it as you can't avoid killing ennmies and do it in the required turns. Here is a video made by myself showing you how to handle the different missions.
If you only need a few levels, you can watch the specific video guide below.
Levels 1-1 to 1-5 :
Level 1-6 :
Level 1-7 :
Level 1-8 :
Level 1-9 :
Level 1-10 :
Level 1-11 :
Level 1-12 :
Level 1-13 :
Level 1-14 :
Level 1-15 :
Update 1 : add video guide for each level.