Swelling and "heat" (local fever) are indications that you've done some damage to the area.
For the first 23ish hours, you want to ice the joint down to help reduce the swelling. You want to work through range of motion exercises to see that the joint operates correctly. After the first 24 hours, you'll want to apply heat to the joint to enhance blood flow to the area to promote faster healing.
Fluid would normally show up later after the injury (several days). However, with any knee injury, i strongly recommend having the injury seen to by a good orthopedic doc (says he of four knee surgeries).
Best to get the jump on any injury, follow the instructions, do the PT and avoid the surgery where ever possible.