what is the connection between igneous rocks and joints & bedding planes?

Question

an explanation of how igneous rocks are formed has to include the terms "joints and bedding planes"

Answer 1

You could discuss some of the characteristics of volcanic rocks.
Columnar jointing in basalt and ignimbrites is pretty spectacular: http://volcano.und.edu/vwdocs/vw_hyperexchange/col_joint.html
The jointing is commonly approximately vertical to bedding surfaces of flows. The orientiation of the joint planes can be measured.
"Bedding plane" most commonly refers to the surfaces of sedimentary beds. However, lava flows, ash deposits, lahars deposits etc. form horizontal layers as well. So, one could describe the surfaces of the layers and measure the orientation of the bedding surface (plane) to understand tilt. The top surface of some lava flows show the polygonal/hexagonal cross-sections of the columnar joints shown above.

http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/rocks/rock_structure/useful_structures.html