Help some parts of my print are missing in slicer

[ThatSkyDude 0]

I'm new to 3d printing and I'm trying to get use to slicers before I get my 3d printer. When i imported my file (.stl), parts of the engines and parts of the cock pit layers were missing, and i have no clue how to fix it. I've added picture the first 3 are from cura of what's wrong and the last 3 are from blender of how there supposed to look, if I need to add more pics for more details ill happily provide.

[ahoeben 1,955]

Here's a good article to read: https://github.com/Ghostkeeper/SettingsGuide/blob/master/resources/articles/troubleshooting/missing_parts.md