You can tell the key from the number of flats or sharps in it.
b = Key of F
bb = Key of Bb
bbb = Key of Eb
bbbb = Key of Ab or G#
bbbbb or ####### = Key of Db or C#
bbbbbb or ###### = Key of Gb or F#
bbbbbbb or ##### = Key of B or Cb
#### = Key of E or Fb
### = Key of A
## = Key of D
# = Key of G
no flats or sharps = Key of C
Good, but each of the key signatures also has a minor key – eg see
https://en.wikipedia.org/wiki/Key_signature
or
https://en.wikipedia.org/wiki/File:Circle_of_fifths_deluxe_4.svg
some of our songs are in minor keys, eg
Hit the Road Jack is in the key of C minor, start chord C minor