How do you read a trill?
Typically, composers notate a trill by writing the letters "tr" directly above the principle note. Sometimes the "tr" is accompanied by a wavy line. Some trill notation consists of only a squiggly line and no "tr" sign at all.
What note do you start a trill on?
Trills almost always start on the note higher than the one that's written. So if you've got a C with the “tr” symbol above it, you'll almost definitely be alternating D-C, starting on D.
Does a trill go up or down?
Forgive me for stating the obvious, but a trill is a rapid alternation between adjacent pitches, up either a half step or whole step from the notated pitch (never down).