Downloads from DAZ are true self installers that are easily recognised, because they come as .exe files (Applications). Just run the file; it will seek out your Poser installation, ask you to agree to the licence, and then do all the work for you. All the folder structure is created, and everything is put in the right place. Remember to read the notice that comes up at the end which tells you where to find your new stuff. You can always re-arrange things afterwards if you know what you're doing and have a tidy mind.

All other downloads (for Windows, at least) will be in the form of a Zip file. Open it up with WinZip and have a look. The easiest type to handle are the ones which have embedded path information, such as the one below. Look at the rightmost column, labelled Path. This should start with "Runtime", as here. If so, carry on to Fully Self-Installing Files.

There may be embedded path information which does not point directly to Runtime, such as this next one. In that case, go to Semi-Automatic Files.

If there is no path information at all, or if the path information does not mention Runtime at all, take a deep breath and go on to Manually Installed Files.