Size of objects

Hi brand new to this software, it looks awesome, but coming from a MECHANICAL background and for many items I want to create I need to try and work out how I know what and how I create items and shapes to specific size. Even some thing simple like a block, how do I make it 100mm cube so when I send it to a printer I get a cube of that size? And say a sphere say 50mm in diameter?
Can somebody help me or point me a tutorial, I have looked over the last few days but cannot find what I am looking for.

I believe Nomad works in “Units” and is not tied to any specific measurement (mm, in., etc.).

What determines the unit’s size is the program you pull your objects into. So, since I typically work with mm in my programs, the units get converted into mm when imported and 1 unit = 1 mm.

Southerngfx is great, but imo he takes foooorevvvvver to explain things. Skip to 3:50 - this is where he starts talking about it.

Thank you for the replies, and for the pointers and suggestions but I am still not grasping the basics of all of this. I will persevere and try and find more tutorials.