These two words are among the most frequently confused in the English language, although their meanings are vastly different.
‘Stationery’ is a noun that refers to writing material and office supplies such as pens, paper, clips, etc.
‘Stationary’ is generally an adjective that is used to describe something that is not moving. For example, a man who is standing in one place can be described as stationary.
The difference in the spellings of the two words can be used to remember their meanings: the second ‘a’ in ‘stationary’ can be thought to stand for ‘adjective’. It is replaced by an ‘e’ in ‘stationery’.