An accidental is a mark used to show a note that is out-of-key. A key signature is a set of "permanent" sharps or flats at the beginning of a piece that tell you what key it's in.
A major, or F# minor
The time signature is placed on the staff between the clef and the key signature.
A natural sign cancels all applicable accidentals in that bar as well as accidentals in the key signature. However, in the case of the key signature accidentals, the natural sign is only applicable to that bar.
Diatonic decoration only uses notes that are in the key signature(white keys on piano for C major). Chromatic decoration uses all notes including those outside the key signature (white and black keys for C major).
A sharp, flat or natural outside the key signature is called an accidental. They are commonly used both for chromatic movement within the song (i.e. sharping the seventh in a minor key when resolving to the first) and for keychanges that will only last a few measures, such as using a run in Csharp to move from C to D.
The time signature is the time and beat of the song, and the key signature is what major or minor it is in
An accidental is a sharp or flat that is not written in the key signature.
Only "B flat" is the key signature, then "C sharp" is the accidental.
No; it is always written as an accidental.
A major, or F# minor
In a major piece, it will sound much more livelier, but in a minor key, it will sound more sadder. like in the piece: Notturno, by Grieg, it is in a minor key, therefore it sounds much more sadder than the piece: Le Petit Negre, by Debussy.
The relative minor key shares the same key signature as its major counterpart but starts on a different note, while the parallel minor key has a different key signature than its major counterpart.
The parallel minor is a minor key with the same tonic as a major key, while the relative minor is a minor key with the same key signature as a major key.
The time signature is placed on the staff between the clef and the key signature.
An accidental is a sharp or flat that isn't in the key signature. For example, if your key signature says that all f's and c's are sharp, and then a G is sharped somewhere in the music, it would be an accidental.
A natural sign cancels all applicable accidentals in that bar as well as accidentals in the key signature. However, in the case of the key signature accidentals, the natural sign is only applicable to that bar.
It shows which notes in a piece are natural, sharp, or flat. Without a key signature, every single accidental would have to be written in instead.