A chromatic scale has evenly spaced pitches. You must play each pitch in the octave, including sharps and flats. An octave is when you play each "natural" note from one note to the same note eight natural notes away. For example, C, D, E, F, G, A, B, C is an octave. A "natural" is the unaltered form of the note, a "sharp" note is pitched slightly higher and a "flat" note sounds lower.
"Enharmonics" are two notes that are written differently but sound the same. For example, there is D and D-sharp, but there is also E and E-flat. D-sharp and E-flat are enharmonic notes, because they sound the same but are written differently.
Starting on C, the notes for a chromatic scale are C, C-sharp, D, D-sharp, E, F, F-sharp, G, G-sharp, A, A-sharp, B and the next higher C from where you started. Descending, the notes are written C, B, B-flat, A, A-flat, G, G-flat, F, E, E-flat, D, D-flat and the next lower C note from where you started the scale. Note where there is an "accidental," or sharp or flat, note between the natural notes. This means each one-octave chromatic scale actually has 13 notes.