Tap the Hammer button in the lower-right corner of the screen to open the Building and Decor Shops.

On the upper part of the screen, you can browse the different sections: Animal Homes, Production Buildings, Trees and Bushes, Exotic Animal Homes, and Decorations.

Tap and hold the Building or Decoration that you want to use.

Drag it over to an empty spot on your farm, then tap the checkmark to place it.

Collect the required materials to complete the construction then tap Build.