Stereoisomers have the same structural formula but the atoms have different arrangements in space.
Optical isomers are stereoisomers that are non superimposable images of each other. They contain at least one chiral carbon, which is a carbon atom bonded to four different atoms or groups.
Optical isomers rotate plane polarised light in opposite directions, anticlockwise and clockwise/right and left, but you can't tell which rotates which way from their structure
For example, these two isomers have the same structural formula but are non super imposible (hoping the picture sent)
Hope that helps, I'm revising it at the minute so if anything's not clear just say
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