There are a couple of ways... for a whole object, select the object and switch to edge mode (this mean all edges will be selected)... right click and select "Hardness"... "Hard"... then "Smooth" this will subdivide the object without changing the shape of the Hard edges. for a face... select the edges you want to create the vertices on... to make one edge between the selected two (on their midpoints) select "Connect"... to make multiple parallel edges... select "Cut" and the number of faces you want to create... this will throw you into vertex selection mode with the new vertices selected... "Connect" will make the parallel edges/faces. I hope this helps... I'm not an expert, but I know this much. :-)