Drier and Dryer are the same word when used as a noun, just spelled differently. The primary meaning of this word is someone or something that makes things dry, especially a clothes dryer or a hair dryer.
My clothes are dry in the dryer.
Mom took out my laundry from the dryer and hung it up to air-dry outside on a line.
There was a dryer in the corner of the room.
I usually hang my clothes out to dry after I wash them, but this time I put them in the dryer.
I purchased a stackable washer and dryer set with my bonus pay.
Currently, both spellings are acceptable, though dryer is more commonly recognized as the correct usage for this noun. Interestingly, drier and dryer were pretty much interchangeable until the middle of the last century when, according to Google's Ngram Viewer, drier as a noun became precipitously less popular:
"Drier" As an Adjective
The word drier is typically used as a comparative adjective, describing something or someone that has less moisture than another thing or person:
A drier climate is one in which the air contains less moisture than a more humid climate.
I was so thirsty that it felt like my throat was drier than the desert.
The weather has been so wet lately, but the drier days are coming soon!
This article is drier than dirt.
My hair is drier than yours because I have a better blow-dryer.
As you can see in the Ngram Viewer below, there is some usage of dryer as an adjective; however, drier has consistently been the more popular spelling .