- Whatever begins to exist has a cause.
- The Universe began to exist.
- Therefore the Universe has a cause.
The first premise is ambiguous because it doesn't specify what kind of "begins to exist" it's talking about. It implies, but doesn't unambiguously state, that it's talking about creation ex nihilo (in other words, out-of-nothing, ie. first there's nothing, then something appears.)
Assuming creation ex nihilo is unfounded because we have exactly zero examples of this. We cannot corroborate that it happens, and even if it happens, if it has a cause, and even if it has a cause, what that cause might be. Simply assuming that it happens and, especially, that it must have a cause, is completely faulty logic. "It makes sense" is not a valid argument for this.
However, when people like Craig try to defend it, they will switch to the other meaning of "begins to exist", which is the more abstract version, ie. energy/matter transforming from one form to another (in other words, for example a table "begins to exist" when the carpenter builds it.)
This is not a distortion or misinterpretation of what, for example, Craig does. This is exactly his argument. In a video, when responding to the objections to the first premise, he directly states things like "didn't dinosaurs begin to exist? Didn't I began to exist?" and then proceeds to belittle the people who present the objection.