@laurabirzu55 Hi! Don't worry, it took me a while to figure this out myself! All those premade lots that come with packs are stored in your library. From your worlds view / manage worlds, select the lot where you want to place something and click the build button in the lower right corner.
When build mode opens, click the Gallery button in the upper right.
In the window that opens, click on the My Library tab and select "Lots" on the left side. Then you can search for specific lots. In this case, I'm placing the "haunted" lot which is called Duplantier Dwelling. So I typed Duplantier and clicked the magnifying glass (not shown) which filtered to the lot below.
Click on that lot to open the lot panel and then click the "Place Lot" button in the lower right.
Whenever you place a lot which has a type different than the existing type, you'll get a prompt asking what type it should be. Here we're placing a Haunted House Residential on a Residential lot, so we need to choose that from the Venue Type drop down menu. This will also give you the chance to choose whether it's furnished or not. I assume you want all the furnishings so after choosing the type, just click the check mark.
Another prompt will say something like "this will replace the lot currently in build mode and this cannot be undone". Just click the check mark to proceed. (You can always add another lot from the library if you want to change it.) And voila, your new lot will be placed! (Note: There have been issues with the lot type not sticking for the Haunted lots and you may have to change this again in build mode after a sim moves in.)
For the other lots like spa and restaurant, you can follow this same procedure and search for them by name but if you don't know the name then you may need to browse the library to find them. I hope this helps!
