Phonetics is a branch of linguistics that comprises the study of the sounds of human speech or in short, it is the study of speech sounds. Although language is obviously composed of sound, speech sounds came to be the main focus of linguistic investigation only in the 20th century. It is concerned with the physical properties of speech sounds (phones), and the processes of their physiological production, auditory reception, and neurophysiologic perception.

Phonetics was studied as early as 2500 years ago in ancient India, with Pāṇini's account of the place and manner of articulation of consonants in his 5th century BC treatise on Sanskrit. The major Indic alphabets today order their consonants according to Pāṇini's classification.

Phonetic transcription is a universal system for transcribing sounds that occur in spoken language. The most widely known system of phonetic transcription, the International Phonetic Alphabet (IPA), uses a one-to-one mapping between phones and written symbols. The standardized nature of the IPA enables its users to transcribe accurately and consistently between different languages. It can also indicate common pronunciations of words.

Phonetics as a research discipline has three main branches:

Articulatory phonetics is concerned with the articulation of speech: The position, shape, and movement of articulators or speech organs, such as the lips, tongue, and vocal folds.
Acoustic phonetics is concerned with acoustics of speech: The properties of the sound waves, such as their frequency and harmonics.
Auditory phonetics is concerned with speech perception: How sound is received by the inner ear and perceived by the brain.

Forensic phonetics: the use of phonetics (the science of speech) for forensic (legal) purposes.
Speech Recognition: the analysis and transcription of recorded speech by a computer system.

Acoustic phonetics is the study of the physical properties of sounds, the air wave frequencies of which sounds consist. The frequency of vibrations measured in hertz; volume of sound measured in decibels. Instruments used to measure and record speech sounds include the sound spectrograph, which produces readouts called sound spectrograms.
Auditory phonetics is the study of how sounds are perceived by the human ear or recognized by the brain. (Mention Oronyms, Monde greens.)
Articulatory phonetics is the study of how sounds are produced by the vocal apparatus. Articulatory phonetics will be the main focus of our study. You need to memorize the anatomical features of the vocal tract shown on the back cover of your textbook.