Consonant design

• Simple consonants: ㄱ, ㄴ, ㄷ, ㄹ, ㅁ, ㅂ, ㅅ, ㅇ, ㅈ, ㅎ
• Tense consonants or glottalized (written as two simple consonants and involve tensing up the mouth): ㄲ, ㄸ, ㅃ, ㅆ, ㅉ
• Aspirated (blowing more air than the simple consonant it's based on): ㅊ, ㅋ, ㅌ, ㅍ
• Consonant clusters (containing two unrelated consonants): ㄳ, ㄵ, ㄶ, ㄺ, ㄻ, ㄼ, ㄽ, ㄾ, ㄿ, ㅀ, ㅄ

The letters for the consonants fall into five groups, each with a basic shape, and one or more letters derived from this shape by means of additional strokes. The basic shapes represent the positions of the tongue, palate, teeth, and throat when making these sounds.

Articulation

Place↓ Manner→	Stop	Affricate	Fricative	Nasal	Approximant
Velar (아음 <牙音> "molar sounds")	ㄱ, ㄲ, ㅋ
Coronal (설음 <舌音> "lingual sounds")	ㄷ, ㄸ, ㅌ			ㄴ	ㄹ
Bilabial (순음 <唇音> "labial sounds")	ㅂ, ㅃ, ㅍ			ㅁ
Sibilant (치음 <齒音> "dental sounds")		ㅈ, ㅉ, ㅊ	ㅅ, ㅆ
Glottal (후음 <喉音> "throat sounds")				ㅇ	ㅎ

Here's a slightly different table:

Articulation

Place↓ Manner→	Stop	Affricate	Fricative	Nasal	Approximant
Velar (아음 <牙音> "molar sounds")	ㄱ, ㄲ, ㅋ			ㅇ
Alveolar	ㄷ, ㄸ, ㅌ		ㅅ, ㅆ	ㄴ	ㄹ
Bilabial (순음 <唇音> "labial sounds")	ㅂ, ㅃ, ㅍ			ㅁ
Palato-Alveolar		ㅈ, ㅉ, ㅊ
Glottal (후음 <喉音> "throat sounds")					ㅎ