Here you can check or uncheck many options.Anyway you must restart DC to take effect.
Colors and Sounds
Here you can set colours and font,nothing important. restart DC++ is required if you change something
Here yopu can save main chat,private chat,uploads logs etc. There's a guide inside DC++ about this option
These are the most important settings on DC++. Take a look to the blue lines. Uncheck the show progress bars,it saves cpu resource.
Check this option to prevent people which continue his download after he leaves the hub. I hate this people!
Check this option for an automatic search for alternative download or source (sometimes TTH search is very important to find the same exactly file)