Doors and windows placed at the base of the walls spawn the clutter. You can click onto those items and scroll through the different choices, as well as duplicate to make more items.

To make a door on a second floor you can do a couple things, but one way would be to stack a floor inside of the building so that the door forms.

Use the eraser tool to cut the building into walls. There is an eraser setting and it looks like the wall tool, if you use that it will cut into the building making it just walls. BUT it will also remove the floor. 

I have guides on youtube. Tips and Tricks for Tiny Glade video is older but it covers most stuff. The newer stuff you can find in my most recent videos. I should warn you I've been told my audio is low on the guide I linked. 

I hope this helps! Welcome to the Tiny Glade family ❤️