How to sing Away in a Manger in your key
Away in a Manger spans 12 semitones (C4 to C5 in its usual key), 44 notes. That's an octave or less, so it fits most voices once it's in the right key.
Words
Away in a manger, no crib for a bed,
The little Lord Jesus laid down His sweet head.
The stars in the sky looked down where He lay,
The little Lord Jesus asleep on the hay.
Finding your key
A song is in your key when its highest note sits at or just below the top of your comfortable range. Measure your range, then move the melody so its top note (C5 here) lands one or two semitones under your easy top. Singsteady does this for you and scores every note as you sing.
1885 words; 1887 tune “Mueller” (James R. Murray). Melody and words are in the public domain. Notes transcribed from the score in Wikipedia, “Away in a Manger” (first score).