Can you explain Thomas Aquinas' account of the "uncaused causer"?

Aquinas' uncaused causer argument plays the role as one of five of Thomas Aquinas' Cosmological arguments for the existitence of God. In essence, this argument can be explained in the following terms. First; every effect, or happening, has a cause; the billiard ball will not roll without the pool cue striking it. Second; we may also say the same regarding existence. Objects do not at one moment not-exist, and then at another moment begin existing; this is just not how our universe functions. It is not so chaotic as this.

So far, this is rather uncontroversial and we can readily accept the two premises without much contention. However, Aquinas then contends that, regarding happenings and existence, causation cannot go back in an infinite regress. i.e. causation cannot simply be relayed backwards in a series of causes and effects ad infinitum. We are left with the conclusion that an uncaused causer must be not only responsible, but necessary, for the first cause. For Aquinas, this uncaused causer was the Christian God. However, we ought to be careful not to attribute qualities to this God that we may have already preconceived. The reason for this is that we can only logically justify a deistic view of causation and effect, if we are to understand it through the lens of Aquinas' uncaused causer.