  We introduce invariant rings for forms (homogeneous polynomials) and for d
points on the projective space, from the point of view of representation
theory. We discuss several examples, addressing some computational issues. We
introduce the graphical algebra for the invariants of d points on the line.
This is an expanded version of the notes for the School on Invariant Theory and
Projective Geometry, Trento, September 17-22, 2012.
