Unfortunately, honest questions are indistinguishable from the horde of transphobes spreading misinformation and sowing uncertainty under the guise of "just asking questions" (sealioning).
If you are genuinely curious, then I recommend starting with the Wikipedia article on puberty blockers, and also reading the one on precocious puberty which is a condition in very young children that is treated by the same drugs. (Tellingly, this usage is non-controversial and exempted from all of the new laws banning puberty blockers for trans children.)