Phonology is the study of phonemes, which are the smallest unit of language without meaning (Cokely & Baker-Shenk, 1997).  In the English language and other spoken languages, the smallest units are sounds.  In American Sign Language (ASL) phonemes are called sign parameters.  

Both spoken English and ASL are articulated.  Articulation refers to how a phoneme (or parameter in ASL) is produced.

In English, spoken language is produced by using different parts of the mouth, tongue, teeth and throat that work together to create sounds.  Some phonemes are produced by blowing air through the bodies articulators, while others to not require air to be produced.  

In ASL, articulation is the physical act of producing a sign.  The act of moving the hands, fingers, arms, facial features and body in specific way.

There are several parameters that work together to produce individual signs-

These parameters help the signer articulate the signs properly.  Tiny changes in a sign can change the meaning completely, as illustrated by both minimal pairs and directional verbs.  Having a large sign vocabulary is also essential to being able to both communicate about a variety of topics and comprehend a variety of topics signed to you.  Some signs are easy to remember, while others are difficult to wrap your head around.  Why?  Because of the differences between both iconic and arbitrary signs.