Correct spelling, explanation: the word using is the present participle/gerund of the infinitive to use. It originates from Old French user. If we want to create a derivative of the verb, we must add the regular -ing suffix to its basic form. Although, the process of derivation is different when the verb ends with the letter -e. Two vowels (silent -e and -i) can’t be put next to each other, so -e must be removed. That’s why the only correct form is using, not useing.

Definition of using:
noun (gerund), taking advantage of a person or situation
Using people is something she usually does.
Michael thinks that using his wife’s inability to refuse him is all right.

Collocations with using:
Some most commonly used collocations include: using one’s head and using the idea/concept.

Incorrect spelling, explanation: useing is a misspelling, but a quite common one. Many English users tend to forget that two vowels can’t occur alongside each other and they don’t remove it while making a derivative form. It’s important to remember that we should always look at the ending of a word. The one and only correct spelling is using.