how did minato seal kurama in himself

Minato sealed Kurama into himself using the Dead Demon Consuming Seal after the Nine-Tails attack, and he split Kurama in half so one half went into him and the other half into Naruto.

What happened

• Minato used the Reaper Death Seal technique to trap Kurama’s chakra.
• Because the full Nine-Tails was too dangerous to keep in one host, he divided it into two halves.
• He sealed one half inside his own body and the other half inside newborn Naruto.

Why he did it

• He wanted to stop Kurama from continuing the rampage.
• He also wanted Naruto to have a chance to grow up with Kurama’s power, instead of Kurama being lost completely.

Important detail

Minato did not keep Kurama sealed in himself for long in a normal way; the sealing act cost him his life, so the seal was part of his sacrifice.

TL;DR: Minato sacrificed himself, used the Reaper Death Seal, and split Kurama between himself and Naruto.