by reflection i assume you want to move components (face, edge, vertex) and move the one that's opposite to it...

if you're making a symmetrical model then you don't need this

just select half the faces on one side and delete them, them when you're done just duplicate special the mesh, then combine, then merge all the vertices at the borders with a low tolerance

you can find examples of that in action all over the place, there are examples of that sort of operation happening in some of kurt's free tutorials here


or maybe you have an asymmetical mesh... in that case you wont find any options of reflection like you could with the sculpt geometry and paint weights tool


if you want to move two components away or closer to each other, then just grab them and use the scale tool (scale in or out)