Simple partials usually feature sensory disturbances or distortions -- migraines, illusions, hallucinations, feelings of dread/nausea, deja vu, jamais vu, etc. Basically, weird feelings.
In complex partials the person has impaired awareness. There can be automatic behaviors like Sue describes -- lip-smacking, wandering round, staring, picking at clothes, saying and doing things without remembering. It's a bit like sleepwalking.
Officially, simple partials are now called "focal onset aware seizures" and complex partials are called "focal impaired awareness seizures", but many people (including my neuro) use the older terms. "Focal" is basically the same as "partial" -- the seizure starts in specific focal points in the brain. Whereas in a tonic-clonic or an absence seizure, the whole brain is involved.