In DAZ Studio 4.x, you can save custom presets in the 'Content Library Pane.'
To do this, first have the scene or figure you want to save. Go to the 'Content Library' Pane. In the Content Library Pane, find the 'DAZ Studio Formats' half. Now find a location in there where you want to save your presets. You can also make your own folders here. To do this, context-click (or right-click) and then choose 'Create a Subfolder.' You can give the 'subfolder' whatever name you like. Click on the subfolder. Now you can save a preset here. On the bottom of the Content Library Pane, look for the plus and minus signs. Click the 'plus' sign and you'll get a huge menu. In the menu, there are several options. The first one is the basic scene file. Choose this and everything in your scene will be saved in a scene file (.duf). Give the scene a name and save. Now you'll see a thumbnail appear in the folder you chose. The thumbnail should have the name that you just gave to it.
You can load that scene or preset in the future by browsing in 'Content Library' Pane to that icon and double-clicking it to load it into the view port.