Here is a very concise version of the Kalam Cosmological Argument:

Things that begin to exist require an external cause. The universe began to exist, so it requires an external cause. As the cause of all physical reality, the first cause cannot itself be part of physical reality, but must be immaterial, non-spatial, eternal, powerful, and personal, which is a basic description of the theistic God.

Here is another way of presenting the gist of the argument without the technical-sounding language:

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