How to make a selection system for parts/models?

[zektonn]

How could I make a selection system for models and parts?

Here’s a video for reference:

Selection thing

Similar to how we do in studio:

Selection thing 2

[2016Richman (wah)]

Here’s a forum with the exact thing you’re trying to do, I believe.

Help with making a selection box

I would like to create a selection box created by the mouse similar to the one in conquerors where you can select troops that are inside the box (already created the troops i just need help with making the box select them) how could i make this? Couldn’t find a post that could help me with this. I don’t have any code here to showcase because i don’t know where to start, i have the box ready but how do i know what troops are inside the box?