Correct spelling, explanation: the origins of this word and its spelling are Latin and French (fr. modelle). The correct form model is thus spelled according to these original forms from older languages. Modle, which may be mistaken because of pronunciation, is wrong.

Definition of model:
1. noun, an object that shows how something should be made or look like
The model of this building looked quite different from the real one.
Disclaimer: this meaning of the word model can also be used as an adjective. Look:
This model building looked quite different from the real one.
2. noun, a person who works as someone to present some products, usually fashion
Mary is a model for the newest Urban Outfitters collection.
3. verb, to create a shape from something; to work as a model
Do you like this clay statue? It’s the first one I’ve ever modelled.
I was modelling a little bit when I was a teenager but never got a serious gig.

Incorrect spelling, explanation: this form is incorrect because its spelling doesn’t go with original forms from Latin, French or Italian (modulus, modelle, modello); the correct form in English is model. Modle may be mistaken though because of similar pronunciation to such words as bottle, spelled with le. However here model is the correct form.