This is the symbol for a metronome. It appears beneath the staff, next to the 'count' numbers, which indicate how to count the time. Large blue numbers represent a count or beat where a note is to be played, while smaller grey numbers are used when notes are either held or not played at all.
This is the symbol for fingering. It appears beneath the staff or tablature and indicates the most practical finger to use for picking each note.
This is the symbol for pick motion. It appears beneath the staff along with a series of a and s symbols that indicate the direction you should pick the notes.