The 8 trigrams seal(double 4 symbol seal) working was unfortunately off-paneled in the manga. However, it should have similar working to Danzo's ura shishou fuin(reverse four symbol seal) judging by the similarity in names
You must be registered for see images
And according to Turrin's translation of the latest databook, he says Danzo's ura shishou fuin is described as a strong version of Shishou Fuin, further cementing the possibility in simiarity in workings and if it really works this way, then even without restrain, it'd be a high difficult sealing jutsu to escape considering both Sasuke and Obito barely escaped it despite warning
According to Obito(the knowledgeable bastard), it was set up to activate when he(Danzo) was about to bite the dust. I suppose he placed the seal command on his body at some point and in Minato's case, probably only has to place a seal command on an object(considering the databook of shishou fuin says it can be used on an object) and set it off when he wants to seal any nearby opponent similarly to how it worked with Danzo. To seal the remaining half of Kyubi inside Naruto, i suppose he put the seal on the baby and it set off to seal anything nearby inside the baby