Forks do actually use oil, at least some do, no such thing as some magic "fork juice". If you have an oil damped fork a simple squirt of teflon oil on the wiper seals keeps things moving, don't use water dispersants like WD40 or GT85.
You need to find out the type of fork you have and download the manufacturers specs form the web page, it could be coil sprung, oil damped and lubricated, air sprung and damped with grease lubrication etc etc.
A very cheap fork will just have stacks of spring and rubber called elastometers inside them slathered in grease, they are the simplest to service, more advanced forks are not a simple or quick job.