Why are you able to distinguish the word zeal from seal? How come you recognize a difference between fool and tool, serve and serve, map and cap, cap and cab?
Looking at different phonological structures, linguists try to make up different classes of sounds to differentiate between them. Phonological structures are classified according to features they have in common or in which they vary, their so-called distinctive features.
Broader classification categories
Consonants with substantial obstruction of the airflow, namely plosives, affricates and fricatives, can be grouped together as obstruents, those without substantial obstruction are called sonorants. Sonorants are nearly always voiced whereas obstruents are usually voiceless (there are exceptions). Plosives and affricates are referred to as non-continuants due to the lack of a continuous airstream in opposition to nasals, fricatives, laterals and approximants, which are grouped together as nasal (nasals) and oral (laterals, fricatives, approximants) continuants (as there is a steady airstream escaping mouth or nose).
The following link leads you to an interactive graphic. This graphic exemplifies different 'Manners and Places of Articulation'. It shows specific tongue and lip positions, voicing and nasality. Try it out to clarify 'Place and Manner of Articulation':
You should also have a look at this website:
Among other features, it contents a step-by-step description and video animation for each English sound.