Incorrect spelling, explanation: the spelling useing is incorrect because when we add suffix -ing to the silent vowel e at the end of the word, we drop this vowel. Thus the only correct spelling of this gerund form is using.

Correct spelling: explanation: a correct form is a gerund form of the verb use. The rule is that when adding suffix -ing to the work ending with a vowel e that isn’t pronounced, we drop this letter. Therefore using is correct and the form useing is incorrect.

Definition of using:
1. verb (gerund form), to make use of something, to adopt something for some purpose
I have been using this backpack for 10 years now.
2. noun, an act of adopting things for a purpose
Using a pencil on a test is not a good idea.