The subject of a gerund is often (but not always) written in the possessive form.
A gerund is a noun made from a verb, they end in "ing". So "using" is a gerund. Phrases with a gerund don't always have an explicit subject, but when they do, the subject can be written as a possessive. In some way, the subject "owns" the action described in the verb. If the "verb" is actually a gerund, and so more like a noun, it makes some sense for the subject to be written as possessive.
So we have:
[Eating a hotdog] made Mark feel sick (the noun phrase in brackets has a gerund with no explicit subject. Implicitly the subject is "Mark"
John eating a hotdog made Mark feel sick. (Explicit subject "John", written as plain noun)
John's eating a hotdog made Mark feel sick (Explicit subject in possessive form)
My eating a hotdog made Mark feel sick (Pronouns have special possessive form)
Both the possessive form and the plain form are possible, but the possessive is somewhat more formal.