Main spellings (~100%)
⟨ng⟩ ~70%
Word-finally and before vowels, the /ŋ/ sound is spelled ⟨ng⟩.
No separate G: In most words, ⟨ng⟩ represents a single sound /ŋ/, not /n/ + /g/. Compare: sing /sɪŋ/ (no G sound) vs finger /fɪŋgər/ (with G sound). The G is only pronounced when followed by another syllable with a vowel.
⟨n⟩ ~30%
Before ⟨k⟩, the letter ⟨n⟩ automatically represents /ŋ/ — you never write ⟨ngk⟩.
N before K: Before the /k/ sound, ⟨n⟩ is always pronounced /ŋ/: think /θɪŋk/, bank /bæŋk/, drink /drɪŋk/. This is automatic — English never spells this as ⟨ngk⟩.