The Cosmological Argument is one of the most popular arguments for the existence of God, and a cornerstone of debate between Atheists and Theists.
It is an old argument, and has been defended by countless theologians from multiple faiths over the centuries. It has various formulations, and many brilliant men have brilliantly defended it against proposed objections from Atheists.
Ultimately, regardless of the particulars of the arguments given from either side, at base, there are only two answers being proposed:
Personally, I do not find attempts to justify clinging to #2 to be worthy of serious consideration. It is intuitive that matter-energy, and natural laws, are the products of intelligence. These things are deaf, and dumb, yet they have properties - mass, charge, behavior, etc. - which demand an explanation. Their bare existence demands an explanation. Also, their continuing to exist demands an explanation.
And, there is no possible explanation for why all of these things exist, and have the properties that they have, other than that they are contingent creations of an intelligent God, who created them, gave them all their properties, and sustains them. There are no other answers which are even possible, as any other alternatives terminate in there being no intellect at the base of this reality, which fails to answer the "why" question that all of creation, with its mere existence, demands to be answered.
Why is there something rather than nothing? Because an uncaused God, who is supremely intelligent and powerful, made it. There is no other explanation for why things exist, and have the properties that they have.
The Cosmological Argument, by itself, is enough. It is a sound argument, and in my opinion, it is best taken simply and intuitively. Let it be enough, and move on to bigger and more interesting questions in life.