I was exercising i jumped up and it sent pain down the back of my calf when i landed. now it hurts to walk downstairs not up. do i have to rest?

Pain in calf: If it goes into the back of the calf and not into the foot, it is probably a sprain of the L5-S1 facet joint or possibly an annular tear of the L5-S1 disc. Either will benefit from regular hot soaks, gentle stretching, and rest. If it goes into the foot then a disc herniation is more likely and the treatment will be the same other than avoiding the stretching.

Could be as: simple as a muscle strain or more serious such as a complete or partial achilles tendon tear. If it doesn't resolve with rest for a couple days with PASSIVE stretching then let your doctor examine it.