There are three main types of letters in Yoruba, which are:

1. Vowels (Iyan) The Yoruba language has seven vowels, which are a, e, ẹ, i, o, ọ, and u. These vowels are pronounced with a clear and distinct sound.
2. Consonants (Abinibi) The Yoruba language has 23 consonants, which are b, d, f, gb, g, h, j, k, l, m, n, p, r, s, ṣ, t, w, y, z, ch, sh, and zh. These consonants can be pronounced as either single sounds or in combination with other consonants.
3. Tone Marks (Àmì ohùn) Tone marks are symbols used in Yoruba to indicate the tone of a word. The Yoruba language has three main tones: high (á), mid (è), and low (à). There is also a neutral tone (ọ̀) that is used when a syllable does not have a clear tone.