Snapping random objects that should line up

Ok, So I own a 3d printer and much of the things I print are others works. I often want to adjust, join or merge objects and I have looked up tonnes of videos of how to do this, but it never works. I am running 2.8 standard settings.

I just need a step by step process to learn how to snap two things together.

https://www.thingiverse.com/thing:525449/

Here are the items I am joining. PLEASE HELP.

Love

A Blender Noob.

Out of interest, how big is your printer?

I joined them but i don’t think they will fit in an average printer, they might also topple over during printing without supports.Complete.stl (256.1 KB)

Don’t know a whole lot about 3d printing, only snapped them together, removed the inner faces and joined the overlapping vertices.

my printer is small but I was going to scale them down. Thank you so much.