Hi, i am new too, also this happened to me, i think you used the option from Edit mesh " extrude faces" instead of "extrude edges", or opposite, if not, like @Skalman said, deleting history might help you.

Just keep in mind what you have selected, edges or faces, in the " Edit Mesh" tab you have extrude for edges and faces, be sure you chose the right one.

The best way is to use the extrude icon in the Polygon toolbar, that icon works for both extrude faces and edges.

To delete history go to: Edit >> Delete by type >> History

Good luck