Is there a way to know, what parts is a preset made of? (e.g. to see for a given preset that it is made of "-10 Saturation" and "+20 Contrast")
Yes. Find the preset file and open it in a text editor. You'll be able to see the adjustments applied.
To find your preset folder, open the Lightroom preferences, click on Presets at the top, then click the Show Lightroom Presets Folder button. This will open the presets folder, then you can go into the Develop Presets, find the one you want, and open the .lrtemplate file in a text editor.
Right click on the preset, select Show In Explorer. Then open the file in notepad or any text-editing program. It will list all the parameters and their values and you can edit this file at will, or create new ones.