F major and its relative harmonic minor, D minor, have only b flat.
It's not too bad, there's only three flats in the key signature; Bb, Eb, and Ab.
Bb is not necessarily an easier key, however it only has 2 flats in its key signature, whereas Ab has 4. So if you're composing for an instrument, the key of Ab would be better.
The key signature is E flat major, which is also, C minor, the relative minor of E flat major. You can find out what flat key signature you're in by finding the second to last flat (in this case E flat). It is the major version of that key signature!
A sharp key signature is one that contains sharps.
A key signature
There is no key signature that has Bb and C#.
The key signature will consist of two flats: Bb, and Eb.
Bb and Eb
It's not too bad, there's only three flats in the key signature; Bb, Eb, and Ab.
Bb, Eb and Ab
One flat, Bb.
Bb is not necessarily an easier key, however it only has 2 flats in its key signature, whereas Ab has 4. So if you're composing for an instrument, the key of Ab would be better.
The key with three flats (Bb, Eb, Ab) is the key of Eb.
1, Bb.
Db Major, or Bb minor.
Bb. B flat has two flats, the first two flats on the staff: Bb, and Eb. Also, the relative minor to Bb, G minor, also contains two flats in the key signature; Bb, and Eb. To find the relative minor to a major key, simply count down 2 and one half steps. ie: Bb, Ab, G, making the relative minor to Bb "G minor", which also has the same key signature.
No key signature could have only Eb and Gb, but some include those two e.g. Db Major, Gb Major, Bb minor and Eb minor.