ROBLOX Unions, how do they work?

This is me info dumping so ... .  

What is a union? A union is something mostly builders use to get more complex shapes WITHOUT using meshes! 

Me personally, i use the for complex floors at most. 

"How do I use one?" 

You need to have 2 objects. One that you want to, chip away, one that will, be your wood chipper to say.  You need to make sure these parts, which they can ONLY be the defaults parts that you can import. (like "Part" , Wedge, cylinder . etc.) Are colliding with each other in some way. 

Go over to your "Model" tab on the top. 

And if you should see an option called "Negate, union," And smt else i don't remember i don't use it!!!

Select one of your items, and hit "Negate" It should turn it red and a lil transparent.  While still selecting your part, hold down shift and select your none negated item. 

Go back to your tab with all the negate stuff, and hit "Union" 

YOU HAVE DONE A UNION!