Keep in mind that content purchased at sites other than the Daz Store do not (as far as I know) contain metadata, so they don't show up in Smart Content, and you'll have to weed through Content Library to find all the components for that product. With that said, here is how I do it:

1. Wherever your "My DAZ 3D Library" is located, either copy your Renderosity files into there, or (as I do) create a separate folder for 3rd Party Content at the same location. Mine is called "My DAZ 3D 3rd Party Library". Your system may vary, but my libraries are located at C:\Daz 3D\Applications\Data\DAZ 3D

2. Unzip the newly purchased content files somewhere, then click through the unzipped folder until you click INTO the "Content" folder. That location should have folders with names like "Runtime", "Data", "People", "Environments", etc (each product is different). COPY all of those folders into the library folder you are using in #1 above. The COPY function will add the new files to existing folders with the same name, or create the folders if they don't already exist. Then delete the unzipped folders and store your original .zip files in an archive somewhere in case you need them later.

Note: I've never known quite what to do with "Templates" zips, so I just unzip them and copy them into a "Templates" folder that I have in each library folder.

3. As others noted above, you need to make sure (just one time) that Daz Studio knows where to look for your content library(s) in #1 above:

* Click on the "Edit" menu, and select "Preferences". A popup window with many tabs will appear.

* In that popup window, click on the "Content" tab. Then click the "Content Directory Manager" button at the bottom of that tab. Another popup will appear.

* In that popup window, click the little plus (+) symbol next to "DAZ Studio Formats", and it will list out the locations where Daz Studio looks for your content.

* Your library(s) from #1 above should be listed there. If they aren't, then click on the "Daz Studio Formats" line so the "Add" button appears to the left, and use that Add function to add the library(s) where your content is located.

* Do the same thing for "Poser Formats" (if you'll be installing older Poser stuff - some of which is really cool)

* Click on "Accept" to save the updated content locations.

4.If the new product DOES support Smart Content, you need to run the Maintenance before Smart Content will recognize it, when you install things manually. (I do this for everything I install from the Daz Store, and never do this for content purchased elsewhere):

* Click on the Smart Content tab

* Click on the horizontal line "hamburger" with the little arrow, right next to the blue "Login..." button at the top of the pane. Select "Content DB Maintenance" from the drop-down menu. A popup for that will appear.

* In the popup window titled "Content Database Maintenance", click the boxes for "Process Metadata Queue" and "Re-import Metadata", and leave all other boxes unchecked. Then click "Accept". That will open a larger popup window listing your Smart Content items. Click "Accept" on that window and wait for it to finish importing the metadata.

5. If you installed products that don't support Smart Content, click on the Content Library pane. Then right-click on "DAZ Studio Formats" and choose "Refresh". Do that again for the "Poser Formats" line. To be honest, I do it for every line there, since I'm not certain how it works. But after those refreshes your non-Smart Content products will show up on the Content Library. Unfortunately, actually FINDING the components can be a real chore sometimes... Good practice is to search for all the components right after you install it, and note the locations of each component in a text file or spreadsheet so you can easily locate them later.

I know that seems like a lot of tasks, but it becomes muscle memory after a while and it only takes a brief moment to install new content once you get used to it!

No need to restart Daz at this point - you should now see your new products in Smart Content and/or Content Library!

For what it's worth, I demonstrate most or all of this in my YouTube video below, though the video itself is an hour long...

https://youtu.be/j9jr373yeh4

I hope that helps!

Paul