Oliver, your stamp would probably be graded as "fine". The stamp is used, quite off center and has a straight edge on the bottom. It catalogs around $1 and is perfectly OK to go in any collection.
However, since you would like to learn, you should look at stamps with a fine eye. To give you an idea, here is the same stamp, graded 98 which is on offer for $1,250 (way overpriced in my opinion, but there it is). Study the differences between this and your stamp and you soon will be able to see what makes a stamp high quality. Look at the centering, the perforations, etc.
